This talk will report on the use of two different photoswitch-containing polymers for metasurface resonance tuning. Each photoswitch can be independently coated on a metasurface, and induce either red- or blueshifts in the metasurface resonance. However, the disparate wavelength tuning of the two photoswitches means they can also be used in combination. We demonstrate that light-responsive photoswitches can be employed alone, or in combination with other stimuli, to add advanced functionality to metasurface resonance tuning and enable potential applications in logic processing or optical neural networks.

Monolayer transition metal dichalcogenides (TMDs) are promising materials for electronics and photonics at highly scaled lateral dimensions. However, their low photon absorption poses a challenge for high-performance optoelectronic devices. We present plasmonic phototransistors (photoFETs) that integrate monolayer molybdenum disulfide (MoS2) with plasmonic metasurfaces, such as Ag, Bi, HfN, and TiN. These plasmonic photoFETs exhibit a significant enhancement in photocurrent compared to pristine 2D photoFETs, enabling high-performance devices with ultrahigh photoresponsivity. The enhancement is achieved through plasmonic nanostructures that enhance light absorption, photo-carrier generation, photo-gating, and hot-carrier transfer rates.

We present two ultra-compact optical components realized by piezoelectric MEMS actuation of metasurfaces: (i) a dynamic waveplate allowing for full birefringence control, and (ii) a novel ultra-compact tunable lens. Integrating metasurfaces with thin-film Piezoelectric lead Zirconate Titanate (PZT) allows for large mechanical displacements (10-70μm) (i.e. capable of strong optical modulations) or fast actuation (⪆ 1kHz), both at low voltage (⪅ 30V) and ultra-low power (50-100nW at 23V). These components are enabling within a wide range of medical applications. A demonstration of our dynamic waveplate for enabling increased contrast under polarimetric mapping of ex-vivo tissue samples will be given.

In this work, based on low-loss single-crystal nanocube-on-mirror plasmonic nanocavities, we demonstrate their electrical integration and the efficient excitation of their plasmonic modes via inelastic electron tunnelling.

Achieving fast and active temporal control of optical metasurfaces remains an open challenge in nanophotonics. Such control would dramatically enhance the scopes of metasurfaces, as their functionalities could be tuned on demand, beyond the limits of their static properties. Here we report on our approach to design and demonstrate the control of all-optically tunable metasurfaces in the ultrafast regime in different scenarios. First, we theoretically predict and experimentally prove by ultrafast transient absorption spectroscopy that spatio-temporal dynamics of hot electrons can promote and control a sub-picosecond photoinduced anisotropy in plasmonic metasurfaces, enabling active reconfiguration of the nanostructure nonlinear response. Then, we demonstrate a giant all-optical modulation of dichroism in an anisotropic all-dielectric metasurface. Finally, we propose a new paradigm exploiting the unique properties of active ultrafast metasurfaces for controlling physico-chemical processes activated by light to improve their efficiency.

The concept of chirality is of utmost importance for the biological functionality of many molecules in the human body and pharmacological compounds. This fact has led to a growing industrial interest into the discrimination of molecular chirality, where the challenge to enhance the intrinsically weak Circular Dichroism (CD) chiroptical effect has been approached from the field of nanophotonics, using metals, high refractive index dielectric materials and hybrid structures with electric and magnetic resonances. Here, we will present our current research on this topic. Using numerical simulations aided by multipole decomposition analysis, we demonstrate how a simple hybrid gold-silicon metasurface can exploit the superposition of several resonances with non-radiating anapole states, providing remarkable conditions for the enhancement of the CD effect in the near-infrared spectrum. We will also show how the usage of these anapole states can be linked to enhanced Third Harmonic Generation, paving the way towards background-free CD signals.

A distinguishing feature of high-index dielectric nanoparticles is their ability to support strong Mie resonances, thereby enhancing the interaction of light with matter and minimizing Ohmic losses, leading to unprecedented efficiency. An important advancement in this field is the investigation of the "transverse Kerker" effect, in which both forward and backward scattering are significantly reduced while lateral scattering is enhanced. We uncover that the realization of a perfect transverse Kerker effect is possible even in passive structures, by exploiting the physics of bound states in the continuum—electromagnetic states remaining localized in photonic structures, coexisting with outgoing waves. Such 'transverse Kerker BICs' are polarization independent, and in momentum space are pinned at the center of polarization vortices with high order topological charges.

Photonic bound states in the continuum (BICs) have enabled a new class of spectrally selective metasurfaces supporting ultrasharp resonances, enabling breakthroughs in higher-harmonic generation, strong light-matter coupling, biodetection, and lasing. However, many implementations still face constraints related to large metasurface footprints, fabrication limits requiring constant resonator heights throughout the structure, or limited numbers of resonances. In this talk, I will present some of our recent concepts for obtaining additional nanophotonic functionalities in BIC-driven systems, including the arrangement of resonators in radial configurations for polarization invariance and reduced footprints as well as height-driven BICs for obtaining maximally chiral light-matter interactions. Finally, I will show how BIC metasurfaces with continuously varying structural parameters can be leveraged to spatially encode spectral and molecular coupling information simultaneously, enabling new perspectives for biochemical spectroscopy.

We demonstrate that incorporating physics-based intuition and Maxwell-equation-based constraints into machine learning process reduces the required amount of the training data and improves prediction accuracy and physics consistency. In addition, physics-based provides an avenue to extend the range of the model applicability outside the space of the original labeled dataset. The proposed approaches are illustrated on examples of photonic composites, from photonic crystals to hyperbolic metamaterials.

Bioinspired photonics is rapidly advancing, leveraging nature's light-managing mechanisms to enhance sustainability, resilience, and processability in nanophotonic applications. A recent breakthrough in the field is the discovery of iridoplast, a chloroplast type with an efficient Bragg reflector structure that boosts light absorption through slow light effects. In this paper, we showcase how all-organic, metal-free photonic structures inspired by iridoplast exhibit optical properties that are thought to be unique to metals or complex oxide compositions. Firstly, we demonstrate that by replicating iridoplast using organic materials, a photonic crystal with Near-Zero-Index (NZI) properties is produced. We show experiments where the organic dye introduces strong absorptions, resulting in an NZI response and photonic stopbands that enhance light absorption in the VIS. Secondly, we show that, with the same materials but a different structure, it's possible to enable Optical Tamm States. Our results demonstrate that photosynthesis is a promising and yet poorly explored source of inspiration for sustainable photonics.

Light-harvesting structures in natural photosynthetic organelles, such as those in purple bacteria, consist of light-responsive chromophores in densely packed antennae systems with organized nanostructures. Inspired by these biological systems, we've created organic materials with densely packed J-aggregates in a polymeric matrix, mimicking the optical role of a protein scaffold. These materials exhibit tunable polaritonic properties from visible to infrared. Drawing from the structure of light-harvesting complexes in purple bacteria, we've studied interactions between light and J-aggregate-based nanorings. Electromagnetic simulations show these nanorings act as resonators, confining light beyond subwavelength scales. These findings enable bio-inspired building components for metamaterials spanning the visible to infrared spectrum in an all-organic platform, offering a fresh perspective on nanoscale light-matter interactions in densely packed organic materials in biological organisms, including photosynthetic organelles.

In the realm of metamaterials, time-varying media have opened new frontiers. By altering material properties at time scales comparable to the oscillation period of light or even shorter, intriguing phenomena like momentum band gaps and parametric amplification emerge. Spatially and temporally modulated materials create four-dimensional metamaterials, offering complete control over light. In this contribution, we present a scattering theory for spatiotemporal metamaterials. It begins with eigenmodes in time-varying homogenous media, addressing light scattering by time-varying spheres. We extend this to 2D and 3D periodic structures using a T-matrix-based approach. These materials constitute spatiotemporal metasurfaces and metamaterials. We introduce theoretical and computational tools, exploring homogenization, resonances, and momentum band gaps. In the latter part, we exploit spatial resonances to lower the required modulation amplitude of the time-varying media to observe a notable momentum band gap. With that, our approach simplifies the experimental observation of time-varying media effects.

We present a versatile mechanism utilizing time-varying metasurfaces for achieving linear frequency conversion, historically governed by nonlinear interactions. Our approach, rooted in invoking linear equations, demonstrates the feasibility of single-frequency conversion through a metasurface, likened to parametric processes found in time-varying systems. Leveraging a generalized time-inhomogeneous convolution product, we introduce an effective nonlinearity furnished by external memory effects, which presents a path that provably adheres to the principles of causality and energy conservation. We explicit the double time-variable electric and magnetic susceptibilities which allow frequency conversion from one frequency to another. The approach can be extended to accommodate multi-frequency conversion by reflection or transmission, as well as full coherence for each monochromatic input. As we anticipate exploring numerical solutions and extension into the quantum regime, we believe this introductory result prepares the ground for future work.

The time crystal is an eagerly sought phase of matter, a many-body strongly correlated system with broken time-translation symmetry and ergodicity. We demonstrate that a classical metamaterial nanostructure - a two-dimensional array of plasmonic metamolecules supported on nanowires - exhibit complex picometer scale dynamics in presence of light. It can be driven to a state possessing all the key features of a continuous space-time crystal: continuous coherent illumination by light resonant with the metamolecules’ plasmonic mode triggers a spontaneous first order phase transition to a superradiant-like state of transmissivity oscillations, resulting from many-body interactions among the metamolecules. The space-time crystal is characterized by long-range order in space and time, broken ergodicity and reduced spectral entropy that are driven by non-reciprocal non-Hamiltonian forces of light pressure.

Here, we characterize the effective response of fully 3D travelling-wave spacetime crystals. To this end, we develop an analytical formalism to homogenize spacetime crystals with spherical inclusions, extending in this manner the renowned Clausius-Mossotti formula to spacetime crystals. Our theory shows that the spacetime crystals behave effectively as bianisotropic materials in the long wavelength limit. Moreover, it reveals the possibility of realizing a purely isotropic Tellegen (axion) response in a system formed by interlaced travelling-wave crystals. We introduce a novel class of media that display invariance under arbitrary Lorentz boosts along a fixed spatial direction. In particular, we prove that the most general class of reciprocal materials invariant under a Lorentz boost is formed by certain biaxial crystals.

In the process of Spontaneous Parametric Down Conversion (SPDC), a pump photon spontaneously splits inside a quadratic nonlinear crystal to signal and idler photons. By spatially modulating the nonlinear coefficient, we form a bulk nonlinear metamaterial that can shape the first and second order correlations of the down-converted signal and idler photons in either the spatial domain or the spectral domains. These degrees of freedom span a multi-dimensional Hilbert space, which is beneficial for quantum information applications. Recently, we have designed and fabricated, using electric field poling, bulk nonlinear metamaterials in KTiOPO4, for generating spatially entangled signal-idler pairs. This includes a bi-photon Bell state in the Hermite-Gauss basis, or a state with 3 dominant pairs of coincidences, approximating a bi-photon qutrit. As for the spectral domain, we generated a variety of quantum states: high purity frequency uncorrelated states, frequency-bin Bell states and frequency entangled bi-photon qudit states. By increasing the pump power, we reach the regime of bright squeezed vacuum sources, enabling the generation of a square cluster state in the frequency domain.

Plasmonic nanostructures can confine light and enhance fields, thus boosting nonlinear optical effects such as second harmonic generation. Our research focuses on the nonlinear effects arising from CdSe quantum dots coupled with plasmonic metasurfaces, made up of cuboid nanoparticles arranged in a rectangular lattice. The study demonstrates a strong reciprocal interaction affecting both linear and nonlinear optical effects, such as photoluminescence, second harmonic generation and white light generation. Thus, our research adds up to the fundamental understanding of nonlinear optical responses from hybrid plasmonic nanosystems.

We develop the vectorial scattering holography approach, as an inverse design method, with both single-channel and multiple-channel regimes for flexibly designing versatile on-chip QE-coupled metasurfaces. Based on the proposed approach, we design, fabricate, and characterize on-chip quantum light sources of two well-collimated single-photon beams propagating along different off-normal directions with orthogonal linear polarizations. Furthermore, we experimentally demonstrate on-chip generation of multichannel quantum emission encoded with different SAMs and OAMs in each channel. The multichannel holography approach is further extended for tempering the strength of QE emission into a particular channel. The holography-based inverse design approach developed and demonstrated on-chip quantum light sources with multiple degrees of freedoms enable thereby a powerful platform for quantum nanophotonics, especially relevant for advanced quantum photonic applications, e.g., high-dimensional quantum information processing.

The topological properties of electronic systems are often linked to the quantization of electric conductivity observed in the integer quantum Hall effect. A precise analogue of such a quantization in optics remains elusive. Here, I bridge this gap between electronics and optics by demonstrating that the response of the Poynting vector to the mechanical acceleration of a medium provides a photonic analogue of the electric conductivity. In particular, I prove that the photonic conductivity determines the energy irreversibly transferred from a periodic mechanical driving of the medium to the electromagnetic field. Furthermore, I demonstrate that for nonreciprocal systems enclosed in a cavity, the constant acceleration of the system induces a flow of photons along a direction perpendicular to the acceleration, analogous to the Hall effect but for light. The spectral density of the photonic conductivity is quantized in the band gaps of the bulk region with the conductivity quantum determined by the gap Chern number.

Here we present a focus variation microscope without moving parts, utilizing the chromatic aberration characteristic of the single-surface metalens. By varying the illumination wavelength filtered through an acousto-optic tuneable filter, scanning of the focal plane can be realised. Imaging is achieved using basic hyperbolic metalens composed of pillars etched from GaN on an Al_2 O_3 substrate. Varying the illumination wavelength from 650 nm to 670 nm shifts the focal plane by 75μm, allowing for capturing the required image stack. Depth information can be extracted by a focus detection algorithm, and the surface topography can be reconstructed. The compact design of this device allows for its use in spaces where traditional instruments cannot fit. We will demonstrate the results from our initial device, including the successful measurement of a stepped artefact, and discuss improvements, such as designing complex multi-element chromatic metalens with enhancing off-axis imaging.

Metasurfaces are artificial optical interfaces designed to control the phase, the amplitude, and the polarization of an optical wavefront. They use physical mechanisms that rely on the coherent scattering of light by nano-scatterers of various shapes and material compositions. In this presentation, I will talk about on-chip integrations of metasurfaces, including lasers, LiDAR and detector arrays, and discuss how these innovative functionalities push the frontiers of optoelectronic systems beyond conventional devices. I will present new imaging capabilities provided by 3D LiDAR metasystem, emphasizing on the unprecedented performances achieved, in terms of frame rate, field of view and the simultaneous acquisition of multiple field of views. Finally, i will present our results on 3D insect-inspired directional imaging devices. We show that mimicking the peripheral vision of insect using planar metalens arrays, we could measure simultaneously the light coming from several directions to reconstruct 3D images. I will conclude this seminar by drawing perspectives and highlighting the opportunities that this field of research still has to offer, both from fundamental and application.

We demonstrate ultrafast tunable, near-infrared to ultraviolet frequency conversion in a chalcogenide glass metasurface based on Mie resonances and quasi-bound states in the continuum resonances, enabled by a phase-locking mechanism between the pump and the inhomogeneous portion of the third harmonic signal. Through phase locking, the pump pulse and the inhomogeneous harmonic component can co-propagate, resulting in the acquisition of the same refractive index and absorption coefficient as the pump. If this process occurs within a cavity, efficient frequency conversion can take place, even in the presence of strong material absorption at the wavelengths of the harmonics. As for all nonlinear processes, a resonant condition at the pump field boosts the nonlinear interactions. Finally, we experimentally show the simultaneous generation of phase-locked structured light beams, including optical vortices and Hopf-links at fundamental and tripled frequencies in all-dielectric nonlinear optical metasurfaces even though the tripled frequency corresponds to the region of high absorption of the dielectric material.

In this work, we introduce an innovative and versatile design strategy that relies on asymmetric Gires-Tournois resonators to enable active full-phase modulation with nearly perfect efficiency. We investigated the complex frequency response of these resonators, identifying the necessary conditions for ideal phase/amplitude modulation response, where achieving unity reflection relies on specific zero-pole position in the complex plane. We explored various active metasurface materials, spanning from silicon to hetero-structured materials, enabling comprehensive phase modulation even with small refractive index changes on the order of 0.01. To address the strong nonlocal effect, we exploited our global statistical learning optimization to fine-tune the refractive index distribution. This optimization resulted in active wavefront shaping designs that surpass 90% in performance. This development holds significant promise for applications in advanced microscopy and LiDAR, pushing the boundaries of optical technology.

We report a theoretical and experimental study of tightly focused vectorial vortex beams propagating through a strongly anisotropic epsilon-near-zero metamaterial. The longitudinal field generated upon focusing can couple to the longitudinal plasmonic resonance featured by the metamaterial with an efficiency which depends on the numerical aperture of the objective, the initial state of polarisation and the quality of the metamaterial. Theoretical predictions and experimental observations prove this interaction to be able to transform any vectorial vortex into an azimuthal beam, aside from the special case of an ideal radial beam. The latter resilience is broken with the introduction of defects in the initial state of polarisation, so that an azimuthal beam is obtained also in the case of non-ideal radial polarisation. We investigate how a change in the metamaterial quality influences the efficiency of the process, as well as its spectral dependence.

The quest for mastering high-power lasers has advanced from initial power scaling to sophisticated beam control. With chirped-pulse amplification catalyzing terawatt and petawatt-scale advancements, the current frontier is refining beam shaping at these extreme powers. We introduce robust monolithic meta-optics, capable of enduring and manipulating high-peak-power laser beams across a wide spectral range, from near-UV to near-IR. These all-glass metasurfaces exhibit a damage threshold at the material's limit, vastly outperforming traditional heterogeneous metasurfaces. We demonstrate the meta-optics robustness with high-peak-power femtosecond pulses. Our nanofabrication protocol allows for precise vertical nanopillars, overcoming previous challenges in tapered sidewalls. We exploit the form birefringence of these nanopillars to induce optical anisotropy in inherently isotropic glass. A geometric perspective underpins our approach to overcoming scaling challenges associated with long-wavelength lasers. Our metasurfaces pave the way for unprecedented control in high-power laser applications.

Metaoptics can provide outstanding solutions for imaging applications in extended depth of field, light field microscopy, and hyperspectral imaging. A series of conventional optical components, such as lenses and mirrors, are employed in traditional optics solutions. In pursuit of a more compact form factor, we demonstrate that the metasurface optics provide key advantages in imaging, such as extreme Extended Depth of Field (EDOF), where the extended DOF range is well beyond what is demonstrated in state-of-the-art. This can be further implemented in a light field microscope to obtain a compact light field microscopy with high-speed volumetric imaging and high spatio-temporal resolution. Finally, I will demonstrate how metaoptic components can be utilized for a compact and efficient snapshot hyperspectral camera model. In all of these examples, we take advantage of end-to-end design. We have developed a fully-differentiable wave optics-based deep learning framework, combining novel hardware (metaoptics) and software (artificial neural computing).

In this talk we discuss the limitations and the potential of metalenses, and demonstrate several results where the limitations are being circumvent by applying a hybrid approach of metalens and computational imaging.

The interplay of strong spin-orbital coupling and inversion symmetry breaking in a Transition Metal Dichalcogenides (TMDC) monolayer induces strong K (K-) valleys spin splitting, yielding two distinct excitonic resonances. While Charge Transfer (CT) and Energy Transfer (ET) phenomena in TMDC heterostructures have been studied extensively, resonant ET between A and B excitons in heterobilayers is less explored. Our investigations reveal resonant exciton transfer from a lower bandgap monolayer WSe2 to higher bandgap monolayer WS2 with a few layers of hBN spacing. Through the excitation at higher energy excitonic states of WSe2, many excitons decay in the B exciton state and subsequently resonantly transfer to the A exciton state of WS2. This resonant ET, distinct from recently reported unconventional ET in TMDC heterostructures at low temperature, eliminates the need for cooling to suppress electron-phonon scattering, enabling an efficient energy transfer process. Our findings offer a novel perspective on utilizing the diverse excitonic responses within TMDC heterostructures for potential applications in optoelectronics and photonics.

Multipole mechanisms of light propagation control and trapping effect in structures composed of dielectric nanoparticle supporting the electric and magnetic optical resonances are discussed. First, a concept of multipole coupling is introduced for explanation what type multipoles and why can be coupled in periodic nanoparticle structures (metasurfaces). Then the implementation of such coupling for light trapping, which does not require any special irradiation conditions for the incident light or geometrical distortion of the symmetry of the periodic structures, is presented. Realization of accidental quasi bound states in the continuum (BICs) associated with multipole coupling is also discussed. Next, magnetoelectric multipole coupling effects in metasurfaces and separate structures composed of particles with bianisotropic electromagnetic response are demonstrated. The presented mechanisms are of a general nature and can be implemented in many structures, which opens up new application prospects.

We study hybrid metasurfaces, where the meta-atoms are combining high index dielectrics with plasmonics metals. This way, we can exploit the coupling between electric and magnetic effects to produce unusual optical responses in the linear and nonlinear regimes. High aspect ratio meta-atoms are required to enhance this magneto-electric coupling, which necessitated the development of a suitable nanotechnology based on the physical etching of the meta-atoms, instead of the more common lift-off approach. The multipolar response of these metasurfaces is also characterized in detail with electromagnetic simulations in order to guide and interpret the experimental results.

Polarization analysis is essential in fields like engineering and biomedical research. Traditional polarimeters use a quarter-wave plate and a linear polarizer but are slow because they rely on mechanically rotating parts. Our team has developed a metasurface-based polarimeter that measures polarization quickly in one shot, without moving parts, using visible light at 640 nm. It combines optical, mechanical, and electrical elements and is precisely calibrated for accuracy. Accompanied by advanced software, it controls operational parameters and captures detailed data. Currently, it matches the speed of existing polarimeters using a CMOS camera for detection. Future upgrades with a fast photodetector array are expected to increase measurement speeds. Our device has been tested against standard polarimeters and can measure both fully and partially polarized light effectively. This new polarimeter is set to change applications needing high-speed, compact polarization analysis tools, offering a leap in rapid and efficient measurement capabilities.

Shaping of short laser pulses offers versatile applications in laser processing, quantum state encoding, ultrafast bio-chemical reactions, and optical communication. Optical metasurfaces have emerged as highly influential and versatile tools for exerting precise control over the properties of incident light. Dielectric Huygens' metasurfaces, in particular, possess the capability to finely tune phase while confining electric and magnetic modes within the resonators, thereby presenting additional prospects, including the exploration of nonlinear effects. In our study, we demonstrate pulse shaping at femtosecond time scale using spatially variant silicon Huygens’ metasurfaces. We experimentally achieve control over pulse dynamics, demonstrating the transformation of a single Gaussian pulse into two pulses as well as into a temporally stretched pulse. The excellent agreement between the measured output pulses and our simulations demonstrates the capability of our metasurfaces to generate precise pulse shapes with femtosecond-level temporal resolution.

Realizing ultrafast optical control of materials is imperative for advancing the field of optical information processing, nonlinear optics, and time-varying materials. Noble metal-based plasmonics has provided many platforms for achieving optical switching, using strong local field enhancement offered by plasmonic resonances and free-electron plasmonic nonlinearity. However, the switching times in such systems are traditionally constrained by the relaxation of photoexcited hot electrons. In this study, we investigate an interplay between electron relaxation lattice vibrations of the nanostructure. This is achieved by harnessing a temporal Fano-type interference between the rapid relaxation of hot electrons and vibrational dynamics within the plasmonic nanostructure. The effect provides high spectral selectivity and sensitivity to the polarisation of light and geometric parameters of the nanostructure. The results are important for development of nonlinear nanostructure with the tailored transient response.

The emission of thermal radiation is a physical process of both fundamental and technological interest. From different perspectives, the emission of thermal radiation can be regarded either as one of the basic mechanisms of heat transfer, as a fundamental quantum phenomenon of photon production, or as the propagation of electromagnetic waves. Focusing on these approaches, here we survey some of the most significant scientific and technological breakthroughs in thermal emission engineering, from fundamental aspects to new phenomena and innovative applications, highlighting the enticing opportunities brought about by transiting from approaches based on spatial modeling to the recent proposal of temporally modulated media.

Effective cross-sections of nano-objects are fundamental properties that determine their ability to interact with light. However, measuring cross-sections for individual resonators directly and quantitatively remains challenging, particularly because of the very low signals involved. In this contribution, we present how we experimentally measured the thermal emission cross-section of metal-insulator-metal nano-resonators using a hyperuniform distribution based on a hierarchical Poisson-disk algorithm. This method relies on the specific properties of hyperuniform distributions, which ensure that no short-range or long-range correlations between resonators disturb the measured signal.

The optical resonances of nanostructures have shown great potential to enhance and control nonlinear optical processes, which are intrinsically weak in ultrathin volumes. There is presently a strong drive towards reconfiguring the resonant response, enabling versatile or broadband functionalities. Among several proposed physical mechanisms (mechanical, thermal,…) all-optical approaches stand out for their fast switching and contactless operation. Pump–probe experiments have demonstrated various forms of intensity-based tuning, exploiting a transient alteration of the material properties. Phase, conversely, has received little attention as a potential control tool. We recently developed a two-pump scheme mixing a pulse at ω with its frequency-doubled replica. The resulting sum-frequency (ω+2ω) and third-harmonic emissions (ω+ω+ω) are coherent and degenerate at 3ω. Because of their opposite parity, their interference is enabled by a symmetry breaking—through directional filtering or by the nanostructure geometry. We reported recently (ArXiv:2307.01794) a 90% intensity modulation and directional routing by an AlGaAs metasurface controlled via the relative phase between the two pumps.

The excitation of quasi-bound states in the continuum (quasi-BIC) in symmetry broken all dielectric metasurfaces have been vastly explored in the last years. The high Q-factor of quasi-BIC resonances make them attractive in sensing, electromagnetic induced transparency or non-linear optics. The resonance wavelength is fixed by the geometry of the metasurface, which is a constraint for applications, which require the tuning of the resonances to different spectral regions. In this work, we demonstrate the use of temperature as a means to fine-tune the quasi-BIC resonance in hydrogenated amorphous silicon (a-Si:H) metasurfaces.

We experimentally implement a novel strategy for dielectric nanophotonics: resonant subwavelength localized confinement of light in air. We demonstrate that individual voids created in high-index dielectric host materials support localized resonant modes that do not suffer from the loss and dispersion of the host medium and are weakly dependent on the void geometry. We show that Mie void modes in dispersive dielectric materials, e.g. silicon, possess a large quality factor, comparable or larger than that for silicon resonant nanoparticles in the visible and UV. We experimentally realize resonant Mie voids by focused ion beam milling into bulk silicon wafers. We experimentally demonstrate resonant light confinement with individual Mie voids from visible down to the UV spectral range at 265 nm. We also experimentally demonstrate a high locality of optical properties of individual voids, which allows implementing them as non-interfering pixels while arranged densely in lattices. Using this property, we further experimentally utilize the bright, intense, and naturalistic colours for nanoscale colour printing.

Plasmonic metasurfaces with sub-5nm dielectric nano-gaps arranged in a large two-dimensional array pave the way to a huge boosting of nonlinear optical effects due to the joint action of a strong field enhancement inside the gap, together with the presence of collective radiative resonances. We studied the nonlinear emission of these metasurfaces in dependence of different gap parameters and illumination conditions. This is a step towards the experimental investigation of nonlinear effects in structures, where light-matter interaction is strongly affected by quantum effects.

In this talk, I will first show our progress on developing passive/static metalenses, which can achieve various unique functionalities such as extremely high (~0.99 in air) numerical aperture or extra-large field of view (~180°). I will also show how by combining multiple lenses and controlling their dispersion we can enable white-light imaging in the visible spectrum and hyperspectral imaging in the mid-wave IR. Finally, I will focus on tunable metasurfaces, particularly demonstrating single pixel tunability in both 1D and 2D pixel arrays, providing the first demonstration of nanoantenna spatial light modulators with ~1 micron pixel size.

Copper presents an alternative plasmonic constituent benefiting from its high natural abundance and low-cost which makes this material very attractive for commercial exploitation. In this work, we present an inexpensive method for the fabrication of copper nanorod-based metamaterial with controllable dimensions and its intrinsic tunable optical properties determined by the geometry of the nanorod array and surrounding media. Copper nanomaterials are often at a disadvantage compared to those produced using noble metals because of their potential for oxidation. Reframing this problem, we developed a procedure for the controllable growth and reduction of copper oxide layers of nanometric thickness via electrochemical oxidation in an alkaline electrolyte at a rate of approximately 0.23 nm/min. The high refractive index sensitivity of these metamaterials enabled the complex electrochemistry of copper to be monitored via in-situ visible light spectroscopy and the subsequent correlation of the optical spectra with the oxidation and reduction processes.

Optical switching has important applications in optical information processing, optical computing and optical communications. The long-term pursuit of optical switch is to achieve short switching time and large modulation depth. Among various mechanisms, all-optical switching based on Kerr effect represents a promising solution. However, it is usually difficult to compromise both switching time and modulation depth of a Kerr-type optical switch. To circumvent this constraint, symmetry selective polarization switching via Second-Harmonic Generation (SHG) has been attracting scientists’ attention. Here, we demonstrate SHG-based all-optical ultrafast polarization switching by using geometric phase controlled nonlinear plasmonic metasurfaces. A switching time of hundreds of femtoseconds and a near-unity modulation depth were experimentally demonstrated. The function of dual-channel all-optical switching was also demonstrated on a metasurface which consists of spatially variant meta-atoms. The nonlinear metasurface proposed here represents an important platform for developing all-optical ultrafast switches and would benefit the area of optical information processing.

Here, we demonstrate low-cost, scalable manufacturing of optical metasurfaces with three approaches: 1) increasing a refractive index of resin with dielectric particle embedding for single-step nanoimprinting, 2) suppressing optical losses of hydrogenated amorphous silicon (a-Si:H) to apply complementary-metal-oxide-semiconductor technologies, and 3) high-index Atomic Layer Deposited (ALD) structural resin. We demonstrate the effectiveness of these materials in creating optical metasurfaces operating at different wavelengths in the infrared, visible, and ultraviolet spectra. Our approaches using PER, low-loss a-Si:H, and hybrid ALD structural resin enables the low-cost, large-area manufacturing of efficient optical metasurfaces across different wavelengths, facilitating the commercialization of metasurface-based photonic devices.

Gallium phosphide (GaP) offers unique opportunities for nonlinear and quantum nanophotonics due to its wide optical transparency range, high second-order nonlinear susceptibility, and the possibility to tailor the nonlinear response by a suitable choice of crystal orientation. However, the availability of single crystalline thin films of GaP on low index substrates, as typically required for nonlinear dielectric metasurfaces, is limited . Here we design resonant monolithic GaP metasurfaces optimized for efficient second harmonic (SH) generation. We experimentally realized the metasurfaces from bulk (110) GaP wafers using electron-beam lithography and an optimized inductively coupled plasma etching process. SH generation measurements show good agreement with numerical simulations and a high NIR-to-visible conversion efficiency reaching up to 10^(-5) for SH emission along the optical axis. Furthermore, we investigated the potential of the suggested monolithic GaP metasurface for SH wavefront shaping applications.

The integration of metasurfaces onto the end faces of optical fibers holds great promise for numerous applications. Traditional top-down fabrication struggles with optical fiber geometry. Our presentation reveals a solution: 3D nanoprinting via direct laser writing to create nanopillar metasurfaces on fiber end faces. This concept gives rise to a novel kind of fiber devices called meta-fibers, allowing for shaping the fiber's output properties. We showcase two applications: (i) achromatic fiber-interfaced metasurface lenses covering the entire telecommunication range, and (ii) meta-fibers generating structured light. These meta-fibers utilize dielectric nanopillars of varying heights, a capability unique to the nanoprinting process.

Hybrid nanophotonic systems consisting of resonant dielectric nanostructures integrated with single or few layers of transition metal dichalcogenides (2D-TMDs) offer important opportunities for active nanophotonic systems featuring an actively tunable response. While the resonant nanophotonic structures serve to enhance the light-matter interaction in the atomically thin membranes, the 2D-TMDs exhibit tunable excitonic properties. However, the experimental realization and demonstration of active functionalities in such hybrid systems remains challenging. Here, we experimentally realize resonant high-index dielectric meta-waveguides and metasurfaces integrated with various species of 2D-TMDs. We demonstrate voltage tuning of the systems’ transmittance and photoluminescent properties, as well as of their polarization dependence. Our results show that hybridization with 2D-TMDs can serve to render resonant photonic nanostructures tunable and time-variant – important properties for practical applications in optical analog computers and neuromorphic circuits.

Optical properties of chalcogenide topological insulators (TIs), namely, Bi₂Se₃ (BS) and Bi₂Te₃ (BT) were studied across the NIR to MIR spectral ranges. In this spectral range, the experimentally measured optical constants revealed an extremely high permittivity values amounting to refractive indices as high as n≈11 and n≈6.4, for BT and BS respectively. These ultra-high index values were then utilized for demonstrating ultracompact, deep-subwavelength nanostructures (NSs), with unit cell sizes down to ~λ/10. Finally, using scattering-type Scanning Near-field Optical Microscopy (s-SNOM), local variations in the optical constants of these nanostructured TIs were studied. Nanoscale phase mapping on a BS NS revealed the role of the imaginary component of the refractive index in the observed phase shifts, varying from as low as ~0.37π to a maximum of ~2π radians across a resonance. This work thus highlights the potential of TIs as a low-loss, high index material for ultracompact nanophotonics.

Flat metaoptics devices are paving a path towards compact and integrated photonics solutions. Composed of engineered subwavelength nanostructures, they offer freedom to shape light and alleviate alignment constraints compared to traditional optics. Utilizing conventional nanofabrication methods, their potential amplifies when combined with on-chip light sources and detectors. In our study, we introduce laser-integrated dielectric metasurfaces tailored for biophotonics applications. Our goal was to sculpt the emission of vertical-cavity surface-emitting lasers by directly fabricating metasurfaces on their emitting facets. Employing unique curved GaAs metagratings, we bypass aspect ratio-dependent etching issues, achieving fan-shaped emission with a ~60° off-axis deflection in both air and glass, with deflection efficiencies of 90% and 70%, respectively. We demonstrate proof-of-principle total internal reflectance and dark field imaging of Au nanoparticles and cells incubated with them. Our illumination module allows effortless toggling between these modes and, since the laser chip is outside the field of view, it is fully compatible with conventional microscopy setups.

Integrating metasurfaces into Liquid Crystal (LCs) cells is a suitable pathway for the realization of tunable optical devices. In such cells, the initial alignment of the LC molecules can be controlled by photoalignment layers. Here, we study the integration of a homogeneous silicon nanocylinder metasurface into an inhomogeneously aligned LC. To locally induce a change in the alignment direction of the LC starting from homogeneous exposure with x-polarized blue light, the photoalignment layers are re-exposed with structured y-polarized blue light. In the spatially-resolved transmittance spectra of the LC integrated metasurface, the double-exposed region can be identified by wavelength-dependent transmittance changes induced by the reorientation of the LC molecules and corresponding spectral shifts of the metasurface Mie resonances. Our results demonstrate that metasurfaces embedded into inhomogeneously aligned LCs allow for the controlled implementation of arbitrary spatial patterns. Possible applications include reconfigurable images, holograms, gratings and Fresnel zone plates.

Possibilities opened when integrating mirrors of piezoelectric micro-electro-mechanical systems (MEMS) and OMSs in the MEMS-OMS configuration with the mirror-OMS separation being electrically controlled are discussed. Recent experimental demonstrations of electrically controlled beam focusing and full-range phase retarders are presented. The latest developments and functionalities demonstrated will also be presented at the conference.

We recently introduced conducting polymers as a new category of materials for dynamically tuneable plasmonics and metasurfaces. Unlike metals, conducting polymers can be dynamically switched between being metallic (negative permittivity) and dielectric (positive permittivity) by varying their redox state. Nanoantennas made from the polymer can therefore provide plasmonic resonances that can be reversibly turned on/off. However, previous reports on conducting polymer plasmonics were limited to p-type polymers. Here, we show for the first time that nanostructures made of an n-type conducting polymer, named poly(benzodifurandione) (PBFDO), can also sustain plasmonic resonances and that are switchable both electrically and chemically. Tandem devices integrated with both p-type and n-type conducting polymer metasurfaces open for novel functionalities including new operation mechanisms based on redox-tunable p-n junctions for dynamic metaoptics. Such dynamic nanoantennas from conducting polymers have prospective applications in reflective displays, smart windows, and dynamic metaoptics including flat lenses and holograms.

Photonic spin Hall effect can manipulate EM waves. One of the most representative manifestations of is spin-momentum locking. The spin changes only when the direction of EM wave propagation changes, offering many applications in photonic devices. Spin-momentum locking can be realized in spoof surface plasmon polariton (SSPP) waveguide. Spin-momentum locking demonstrates that photonic spin Hall effect (SHE) can manipulate electromagnetic (EM) waves, however, programmable EM wave manipulation is still challenging. In this work, the spin-momentum locking in programmable plasmonic metamaterial is demonstrated. Digital coding spoof surface plasmon polaritons (SSPPs) waves have two transverse spins. Moreover, photonic spin logic devices based on programmable plasmonic metamaterial are developed. By implanting spin degrees of freedom in digital coding SSPPs, both spin and coding can be used to control energy flow. Furthermore, SSPPs logic “AND” gate and “NIMPLY” gate (A AND NOT B) are designed and verified by simulation and experiment. The combination of digital coding technology with photonic SHE provides a more powerful and flexible platform for controlling EM waves.

Conventional approaches to create optical beams with Orbital Angular Momentum (OAM) tend to rely on bulky optical systems and external laser sources, limiting their use in integrated photonics. Metasurfaces provide a solution for compact on-chip generation of OAM beams, which is crucial for the broad implementation of OAM technologies. This work will present the design and fabrication of metasurfaces consisting of amorphous silicon nanopillars on a sapphire substrate, which is used to generate OAM beams from an impinging Gaussian beam at 1250 nm wavelength.

The creation of smart and autonomous manufacturing chains is reliant on the development of suitable sensors to provide the feedback required, improving the quality of the parts made, reducing scrappage and allowing bespoke one-off items to be manufactured right first-time every-time. Optical measurements would seem ideal for just such applications, however the optical instrumentation that is employed to take them is often far too large and heavy for deployment where they would be of most use, and the use of traditional refractive elements limit the size and weight reductions that can be achieved. Here we present our work on using metasurfaces to overcome just such problems, developing a miniaturized chromatic confocal sensor by exploiting the chromatic aberration found with a basic hyperbolic metalens to our advantage. Further we show how the range and resolution of this device can be modified through design, delivering a compact, rapid, and highly practical sensor.

Advancing an Optical Metasurface (OMS) platform with dynamic adjustability and rapid response times strongly aligns with the current trends in photonics. Firstly, we demonstrate an electrically driven MEMS-OMS-based dynamic linear polarizer (DLP), benefiting from a tunable hybrid plasmonic Fabry-Pérot (FP) cavity formed by an anisotropic plasmonic OMS and thin-film piezoelectric MEMS mirror and featuring a continuous and tunable, in a fast and reversible fashion, Extinction Ratio (ER) between two linearly polarized incident beams. DLP-based dynamic grayscale imaging and Vector Vortex Beam (VVB) generation have also been realized. Secondly, we embark on an in-depth exploration of optical Exceptional Points (EPs) within a fully electrically tunable non-Hermitian metasurface platform that leverages the synergistic interplay between chiral gold meta-atoms with a piezoelectric MEMS mirror, thereby allowing for fine-detuning the system to construct a voltage-controlled spectral space. We demonstrate a voltage-controlled topological phase transition, transforming a chiral EP to a Diabolic Point (DP) characterized by degenerate eigenvalues and orthogonal eigenstates.

We study the optical properties of hybrid silicon-gold nanocylinders and show that the internal material inhomogeneity can lead to their strong bianisotropic response associated with the distortion of their symmetric properties. The spectral response of the metasurfaces composed of such particles can have narrow resonance features associated with resonant multipole coupling and excitation of quasi-BIC states. We demonstrate that the metasurface resonant features are accompanied by the field enhancement in the metasurface plane and strongly depend on the polarization of the incident waves. The latter circumstance makes it possible to implement switching control of the resonant response of metasurfaces by changing the polarization of the incident wave.

This work reports the high-resolution aluminum (Al)-based plasmonic devices in the near-infrared region with incorporation of metamaterials. Our quantitative findings under angle interrogation reveal a notable enhancement in the detection accuracy and quality factor due to incorporating a metamaterial layer over conventional plasmonic structures. The proposed final plasmonic device comprises a Metal-Dielectric-Metal (MDM) configuration with Al metal and Barium Titanate (BTO) as the high dielectric constant material. A monolayer of molybdenum disulfide (MoS2) serves as the binding medium and is utilized to increase the adsorption of biomolecules on the sensor surface. The engineered plasmonic device is used for the detection of cervical (HeLa), blood (Jurkat), adrenal (PC12), and breast (MDA-MB-231 and MCF-7) cancer cells and offers a sensitivity of 101.2 o/RIU and a figure of merit of 5060 RIU-1. The integration of metamaterials into plasmonic sensors holds transformative potential for the field of biomedical sensing.

Surface Lattice Resonances (SLRs) found in uniform plasmonic metasurfaces feature high Q-factors, enabling applications in sensing and nanolasing. To scale up their production, we introduce the Capillary-force-Assisted Particle Assembly method (CAPA). It allows to assemble colloidal nanoparticles onto patterned templates. We demonstrate large hexagonal and square lattices comprised of single-crystal Ag nanoparticles with high quality SLRs. They can be excited into optomechanical oscillations which modulate the LSPR and in turn the SLR over time, giving the metasurface intriguing properties in the ultrafast regime. Moreover, we tailored the SLR to match the excitation wavelength used in Raman spectroscopy. This allowed to create SERS substrates with improved performance, achieving 100 times higher sensitivity at the target wavelength. Finally, we interfaced plasmonic metasurfaces with gain media and registered room temperature nanolasing. The demonstrated applications showcase the versatility of CAPA and we expect self-assembly to play a major role in the development of large scale metasurfaces and nanophotonics devices.

Meeting the increasing demand for cost-effective Metamaterial (MTM) devices poses a challenge, particularly in creating a straightforward and polarization-independent interfacial water heating device due to the nanoscale dimensions involved. Our proposed solution addresses this challenge through uncomplicated designs, incorporating basic geometric shapes as MTM inclusions to form metal-insulator-metal combinations and periodically arranged metal-insulator layers. By employing high-loss materials such as Nickel and Tungsten as metal inclusions, we have successfully demonstrated substantial Electromagnetic (EM) wave absorption within the 400 nm to 1600 nm range, achieving over 80 percent absorption across the visible to infrared spectrum. Additionally, we introduced liquid crystal layers to the Metal-Insulator-Metal (MIM) structure, providing tunability and expanding the device's usability across a wider range of the EM spectrum. Regarding fabrication and optimization for mass production, these designs have the potential to serve as valuable additions to interfacial heating devices. Acknowledgement: This work is supported by the Israel Ministry of Science and Technology.

We propose an easy-to-fabricate one-dimensional subwavelength grating as an optimized metamaterial for the excitation of quasi-bound states in the continuum in the near-infrared. Experiment measurements and numerical simulations are in excellent agreement with the presence of near-infrared resonances with a high-quality factor (up to 10⁶) accompanied by a significant increase in electric and magnetic fields (in the order of 10⁴), that can be exploited in many applications in photonics.

We explore the application of a single-step nanoimprinting technique using water-soluble Polyvinyl Alcohol (PVA) to fabricate tunable metasurfaces. These metasurfaces display multiplexed structural color and meta holography. The structured PVA achieved below 100 nm, accompanied by aspect ratios approaching 10. Under increasing relative humidity conditions, the PVA metaatom can expand by approximately 35.5%, allowing precise control of wavefronts. Here, we demonstrate the optical security metasurfaces for multiplexed encryption, capable of revealing, concealing, or eliminating information based on changes in relative humidity, both irreversibly and reversibly.

The single-beam MOT system based on the diffractive optical element offers a new route to develop compact cold atom sources, which, however, suffers from the low optical efficiency and unbalanced beam intensity distribution. To solve this issue, we developed a centimeter-scale dielectric metasurface optical chip with dynamic phase distributions, which was used to split a single incident laser beam into five separate ones with well-defined polarization states, high efficiency and uniform energy distributions. The measured diffraction efficiency of the metasurface is up to 47%. A single-beam MOT integrated with the metasurface optical chip was then used to trap the 87Rb atoms with numbers approximately 1.4 × 10⁸ and temperatures approximately 7 μK, exhibiting better performance in cooling and trapping of atoms compared to the grating MOT and the early version of the metasurface MOTs.

The Giant Magellan Telescope will employ laser tomography adaptive optics, using laser guide stars to measure and correct wavefront distortions with a high sky coverage compared to natural guide stars. A laser guide star is the resonance fluorescence induced by a launch laser propagating through a column of the atmospheric sodium layer, with narrowband emission at a 589nm wavelength. The column shape results in the laser guide star having observable elongation depending on perspective. Shack-Hartmann wavefront sensing remains challenging as the elongated axis of a subaperture focal spot can be as large as 10-14''. Currently, detectors with a large number of pixels are used to compromise between sensitivity and accuracy. We propose a novel approach based on a metasurface lenslet array, where each subaperture has a custom anamorphic ratio and orientation. Two metasurfaces with sub-wavelength-thick nanopatterned layers of TiO2 separated by a 6.5mm air gap accommodate a fixed focal length of 8mm and anamorphic ratios up to 1:10, as confirmed by Optics Studio simulations. We identify the experimentally feasible metasurface design suitable for the established nanofabrication approaches.