With the proliferation of networked sensors and artificial intelligence, there is an increasing need for edge computing where data is processed at the sensor level to reduce bandwidth and latency while still preserving energy efficiency. In this talk, I will discuss how meta-optics can be used to implement computation for optical edge sensors, serving to off-load computationally expensive convolutional operations from the digital platform, reducing both latency and power consumption. I will discuss how meta-optics can augment, or replace, conventional imaging optics in achieving parallel optical processing across multiple independent channels for identifying, and classifying, both spatial and spectral features of objects.

Quasi-2D perovskites have gained significant attention in the field of optics and photonics recently due to their intriguing optical properties. Endowed with optical properties typically found in both 2D and 3D systems, they offer a premier platform for tunable optical devices. Here we studied the prospects of Quasi-2D perovskites for lasing by first delving into excitonic and free carrier ultrafast dynamics, exploring into random lasing from naturally formed cavities in planar films and investigating lasing from structurally-tuned nanowires. Our results give insights on the fundamental radiative processes in these novel materials and build a foundation for future experiments and applications.

The ability to distinguish between different states of a given cell, as well as between different types of cells, is crucial for a variety of fundamental and clinical life sciences applications. Those include: monitoring biochemical processes, detection of the drug effects, and real-time non-pertubative imaging of living cells. I will describe an experimental technique developed in our lab – Metasurface-Enhanced Infrared Reflection Spectroscopy (MEIRS) – used to produce chemical images of evolving live cells with diffraction-limited spatial resolution. Different types of metasurfaces used in this study will be described, including flat two-dimensional, three-dimensional meta-on-dielectric, and multi-resonant plasmonic metasurfaces

I will discuss the design and implementation of space plates and space optics, which are space plates with position-dependent responses. I will show how new variants in gradient-based topology optimization can yield space plates with enhanced compression factors, sizes, and efficiencies compared to conventional designs. I will also show how space plates and space optics can be co-designed with refractive optical systems to yield imaging systems with new capabilities and form factors. These concepts showcase the emergent capabilities of multi-scalar optical systems that combine the synergistic properties of macroscopic and subwavelength-scale structured media.

Optical imaging techniques are the most commonly used methods in biology and medical research. Nano-photonics, the emerging optical techniques, with unique optical capabilities to manipulate the basic characteristics of light have recnetly received a significant amount of interest in the field of optical microscopy and endoscopy. This talk will introduce the latest studies on the biomedical use of structured light, as well as metasurfaces. In addition, structured light plays vital roles to enhance resolution. The following are the topics that will be covered: optical microscopy, light sheet microscopy, optical endoscopy, and deep learning. This talk will also discuss the technological challenges presently encountered with metasurface from the point of view of preclinical and clinical systems.

The ability to locally control incident light's polarization state is one of the primary distinguishing factors between metasurfaces and past generations of diffractive optical elements. Polarimetry, the measurement of light’s polarization state, can benefit from the metasurfaces which sort light based on its polarization into several channels enabling polarimetry with a minimum of optical components. Here, we present a wide field-of-view polarimetric imager integrated on a single glass substrate. The device captures polarimetric images over a 40 degree field-of-view in a 10 nm bandwidth in the near-IR around 870 nm and consists of polarization-sensitive metasurface diffraction grating (for polarimetry) and a metalens-aperture stop system (for imaging). Imaging polarimetry with this camera is demonstrated and practical considerations surrounding this approach are discussed.

We aim to address one of the fundamental limitations of machine learning (ML): its reliance on extensive training datasets by incorporating physics-based intuition and Maxwell-equation-based constraints into ML process. We show that physics-guided networks require significantly smaller datasets, enable learning outside the original training data, and provide improved prediction accuracy and physics consistency. The proposed approaches are illustrated on examples of photonic composites, from photonic crystals to hyperbolic metamaterials.

We report an experimental validation of a machine learning-based design method that significantly accelerates the development of all-dielectric complex-shaped meta-atoms supporting specified Mie-type resonances at the desired wavelength, circumventing the conventional time-consuming approaches. We used machine learning to design isolated meta-atoms with specific electric and magnetic responses, verified them within the quasi-normal mode expansion framework, and explored the effects of the substrate and periodic arrangements of such meta-atoms. Since the implemented method allowed for the swift transition from design to fabrication, the optimized meta-atoms were fabricated, and their corresponding scattering spectra were measured using white light spectroscopy, demonstrating an excellent agreement with the theoretical predictions.

The field of nanophotonics is based on the ability to confine light to sub-diffractional dimensions. In the infrared, this requires compression of the wavelength to length scales well below that of the free-space values. Two predominant forms of polaritons, the plasmon and phonon polariton, which are derived from light coupled with free carriers or polar optic phonons, respectively, are broadly applied in the mid- to long-wave infrared. Within anisotropic materials, these optical modes can be induced to propagate with different wavevectors along different axes, or even be restricted to propagate only along a single direction. Here, we discuss the influence of crystalline anisotropy in dictating the polaritonic dispersion, including highly directional hyperbolic shear polaritons in low-symmetry monoclinic and triclinic crystals, as well as the ability to control the wavelength and propagation direction of these modes using free-carrier injection and twist-optic concepts. Further, we highlight how such phonon polaritons can be employed as ultrafast and efficient carriers of thermal energy, providing alternative dissipation pathways for heat.

This study investigates the thermal optical coefficient (TOC) of Si, SiNx, SiO2, and TiO2, establishing a comprehensive database across temperatures (20°C-80°C) and wavelengths (400nm-1800nm). This dataset informs the design of anti-thermal optical devices. For instance, utilizing TOC disparities at 1550nm, we developed an anti-thermal quarter-wave plate optical mirror with Si and TiO2. This innovative approach harnesses material-specific thermal responses, showcasing potential applications in designing reliable optical platforms. Our research contributes not only to understanding TOC variations but also provides a practical foundation for advancing anti-thermal optical technologies.

Type-II superlattice (T2SL)-based detectors as a new platform for mid-IR detectors, aiming to bring the performance of state-of-the-art HgCdTe based designs to room-temperature operation. T2SLs provide a way to highly reduce detector thickness when a thin T2SL layer is implemented in a multilayer core combined with a dielectric metasurface that uses guided mode resonance (GMR) to couple the incoming light into the detector. However, supporting a GMR requires the detector to have significantly expanded spatial area, potentially preventing the creation of truly compact finite detectors. In this work we propose a possible solution to this problem. The proposed design of a detector relies on the reflective metasurface to couple incident light (λ_0) into a guided mode that overlaps T2SL absorber layer. Our analysis demonstrates that the width of the detector must be at least ~20λ_0-wide to achieve ~60% external quantum efficiency (EQE), with narrower detectors exhibiting decreased performance. To counteract this, we propose a design that combines the benefits of GRM and Fabry-Perot cavity enhancement, resulting in 2λ_0-wide, subwavelength-thick detector that in theory achieves ~51% EQE.

Keynote: We witness the growing excitement and breadth of research on Time Crystals. I argue that nanophotonics can play a pivotal role in bringing this sophisticated, yet esoteric subject to the domain of “timetronics” – an information and data technology relying on the unique functionalities of Time Crystals.

Recently, the emerging field of time-varying photonics has called for a broader theoretical framework to include the effects of temporal variations on light-matter interactions. A notable development in this context is the photonic temporal crystal, whose optical properties are modulated in a time-periodic manner. A distinctive feature of these crystals is their non-Hermitian band structures, which lead to momentum gaps with non-Hermitian degeneracies, or exceptional points, at their edges. In this talk, I will discuss how the spontaneous emission rate is net positive at the momentum gap frequency. This observation highlights the importance of the non-orthogonality of photonic Floquet eigenstates and brings the Petermann factor into focus in the context of photonic temporal crystals.

Structured light is important in various fields including metrology, optical trapping, communications, and nonlinear optics. Here, we introduce a method to manipulate cylindrical vector beams using a strongly anisotropic epsilon-near-zero metamaterial. The longitudinal and transverse fields of a vector beam interacts differently with the metamaterial due to its anisotropy with an efficiency which depends on the numerical aperture of the objective, the initial state of polarisation and the quality of the metamaterial. These anisotropic interactions lead to reshaping the vector beam and its polarisation as demonstrated experimentally and theoretically. The approach facilitates wave front shaping and spatial polarization engineering, promising applications in microscopy, information encoding, and biochemical sensing.

The field of metasurfaces has opened tremendous new opportunities in many areas of optics, photonics, and electromagnetics. In this talk, I will discuss our recent research efforts on two emerging classes of metasurfaces that leverage new degrees of freedom, namely, “time” and “wavevector,” with a focus on their theoretical aspects and the new opportunities they enable.

Time interfaces, which arise when an abrupt change in the properties of the host material occurs uniformly in space, have opened interesting opportunities for extreme wave manipulation, e.g., amplified emission and lasing in photonic time crystals (PTCs). Yet, altering the material properties is conventionally limited to active systems, which suffer from instabilities or saturation. In this talk, we introduce a passive path to achieving time interfaces in a switched transmission-line metamaterial. We first discuss the experimental evidence of distinct temporal boundary conditions at such passive time interfaces. Combing these unusual temporal discontinuities periodically, we then introduce passive PTCs. Unlike conventional PTCs where waves are exponentially amplified inside the momentum gaps, we demonstrate that PTCs can be achieved without parametric amplification, featuring stable momentum bandgaps. The passive PTC not only behaves as an anti-laser in time but also features momentum-filtering responses. This feature may establish a building block to realize functional time-metamaterials, with opportunities for extreme spacetime wave control, e.g., real-time waveform shaping.

The speed of transfer of mass may not be greater than the speed of light, however, the apparent motion of objects may be superluminal. Space-time modulations of a surface that exhibit superluminal motion have been the topic of myriad theoretical investigations that promise nanoscale control over electromagnetic waves via the Doppler effect and Fresnel drag. Herein, we use the ultrafast photoexcitation of a 40 nm film of Indium Tin Oxide to generate superluminally travelling modulations, which act as diffractive apertures in both the spatial and temporal domains. By designing continuous and discrete forms of motion we realise a tuneable platform for generation of complex momentum-frequency beam profiles and exploring exotic phenomena like hawking radiation.

In this study we explore strong coupling of polariton modes within patterned 2D Van der Waals materials and optical cavities, a frontier promising transformative advances in nanoscale light-matter interactions. Utilizing a quasistatic eigenmodes expansion approach, we develop a theoretical framework that bridges quantum and classical analyses, enabling precise manipulation and prediction of polariton behavior. This study not only elucidates the impact of pattern shape and material properties on these interactions but also establishes a crucial connection between the quantum and classical realms. Our findings pave the way for novel techniques in engineering optical phenomena, offering significant insights into the intricate dynamics of polaritons in 2D material systems, with potential implications for next-generation photonic and quantum technologies.

We will report on our investigations of laser-induced dewetting (in the cw and fs regimes) on thin metallic films deposited on substrates with different nonlocal optical environments. We observed that the morphology of dewetted plasmonic nanostructures is affected by incident pulse duration, and by the nonlocal optical environment. In addition, we will report on a broader effort on understanding mechanisms of short-pulse-induced damage on several materials and structures such as metallic/refractory thin films and metasurface components. We will also present on laser beam shape engineering efforts for damage mitigation in fused silica optics, for applications in extreme environments. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. 24-FS-015. LLNL-ABS-861157.

We demonstrate a novel method for effectively coupling light with surface-plasmon polaritons using specially designed dipolar scatterers strategically positioned at an optimal distance from the surface. In our experiments, we constructed gold disks with a silica spacer from a flat gold surface and adjusted the spacer thickness to match a specific scatterer geometry that resonates at a predetermined optical frequency. This setup achieved a peak coupling efficiency of light to plasmon that is comparable to the square of the light's wavelength, at an ideal distance facilitated by the balance between strong particle-surface interactions and minimal surface-induced particle-dipole damping, both of which are enhanced at closer distances. Our findings, which are consistent with both analytical theory and electromagnetic simulations, propose the use of strategically placed scatterers as an innovative solution to the longstanding issue of efficient coupling in and out of nanophotonic systems.

We present 3D printed microoptics as a tool for quantum technologies. Specifically, when coupling single photons from quantum emitters into single mode fibers and when coupling single photons from single mode fibers into superconducting single nanowire detectors, 3D printed microoptics enables emission collection, mode conversion, and efficient coupling from one device into the other. We demonstrate different solutions which include 3D printed optics directly onto single mode fibers, as well as onto no-core fibers spliced onto single mode fibers. We also present solutions for the emission collection and recollimation of different quantum emitters such as semiconductor quantum dots or defect centers [1]. Furthermore, we demonstrate how 3D printed optics can be utilized to focus the photons of a single mode fiber down to an extremely small active area of a superconducting single nanowire detector, which can enhance its detection speed due to reduced capaticance and kinetic inductance [2]. Finally, we also demonstrate how 3D printed optics on single mode fibers enables coupling of light to single trapped atoms inside of a vacuum chamber [3]. [1] M. Sartison, K. Weber, S. Thiele, L. Bremer, S. Fischbach, T. Herzog, S. Kolatschek, M. Jetter, S. Reitzenstein, A. Herkommer, P. Michler, S. Portalupi and H. Giessen, “3D printed micro-optics for quantum technology: Optimised coupling of single quantum dot emission into a single-mode fibre”, Light Adv. Manuf. 2, 6 (2021). [2] S. Mennle, P. Karl, M. Ubl, P. Ruchka, K. Weber, M. Hentschel, P. Flad and H. Giessen, “Towards fiber-coupled plasmonic perfect absorber superconducting nanowire photodetectors for the near- and mid-infrared”, Opt. Continuum 2, 1901 (2023). [3] P. Ruchka, S. Hammer, M. Rockenhäuser, R. Albrecht, J. Drozella, S. Thiele, H. Giessen and T. Langen, „Microscopic 3D printed optical tweezers for atomic quantum technology”, Quantum Sci. Technol. 7, 045011 (2022).

Transitioning to all-inorganic cesium perovskites is an alternative route to tackle the long-term stability challenges in perovskite solar cells (PSCs). CsPbBr3 perovskites offer robust stability and do not suffer from polymorphism relative to its counterpart, CsPbI3. With a Shockley-Queisser single-junction limit of ~ 16 % and a wide bandgap of ~ 2.3 eV, it is attractive for semi-transparent, building-integrated photovoltaics and multijunction applications. Here, an all-vacuum-processed all-inorganic PSC is demonstrated to achieve a phase-pure, compact film of the desired thickness, paving the way for exploring the CsPbBr3 active layer in other optoelectronic devices such as LEDs.

Applications such as quantum computing or quantum sensing, have the potential to revolutionize many industries and pave the way for a new era of groundbreaking capabilities across various important fields such as medicine and material-science. To scale these applications up to the point where they can address real-world industry relevant problems, the development of high-efficiency photon extraction and coupling interfaces is crucial. In this work, we explore the use of micro-optical beam shaping interfaces to facilitate the extraction of light from points emitters which are fundamental unit blocks for many of these quantum technology applications.

Silicon photonics for telecommunication applications has garnered much attention recently. The optical transparency and the large refractive index contrast of silicon in the telecommunication wavelengths allow the implementation of high-density photonic integrated circuits. The drawback of silicon photonics is that there is no native efficient light source. Integration of III-V material, which offers outstanding optical emission properties, on silicon provides a potential solution. One of the approaches for large-scale integration is through heterogeneous integration of a III-V membrane using adhesive bonding. Here, we will report on the integration of telecom C-band emitting InAs QDs on a silicon platform through such bonding.

Spin defects in diamond are a promising candidate for quantum information processing applications. One of those is the tin vacancy (SnV) defect in diamond. It shows an individually addressable spin, bright emission into the zero phonon line (Debye-Waller factor of 0.6) and a large ground state splitting, enabling it to work at relatively high temperatures of 2 K. So far, it has been challenging to create stable SnV centers and incorporate them into nanophotonic devices. In this work, we report on the successful generation of bulk SnVs and integration into nanophotonic structures. The implanted SnV show stable PL and PLE spectra in bulk and nanostructure.

In this work, we design neural network architectures, including fully connected neural networks (FC) and convolutional neural networks (CNN), to solve forward design problems. We show that FCs and CNNs can predict the acoustic response based on the positions of cylindrical scatterers. These networks develop regressor models for approximating the absolute acoustic pressure at a focal point. A comparative study between the two networks is conducted against exact results from multiple scattering theory. We implement the FC and CNN models to simulate acoustic multiple scattering from cylindrical structures. While CNNs are computationally intensive, they perform better by leveraging spatial correlations between scatterers. This study tests the model's applicability to our problem. Numerical examples of pressure amplitude prediction at the focal point using random planar configurations of cylindrical rigid scatterers in water are presented. Results from deep learning models are compared to semi-analytical solutions from multiple scattering theory, with computations performed on MATLAB.

In this talk I will explore the hidden potential of electrochemically actuated metasurfaces. Electrochemical actuation is unique in that it provides for control over both the volume expansion of a scatterer as well as the free electron density for permittivity control. I will explore this freedom in dynamic tuning of titanium dioxide and silicon-based metasurfaces, materials already popularized in the field of photonics for their high index and low loss throughout the visible spectrum. Using these materials, we leverage electrochemical intercalation of lithium to initiate phase changes in a continuously tunable, reversible, and bi-stable manner, using bias voltages that are an order of magnitude less than similar devices.

Sub-wavelength structuring of semiconductors has recently provided a powerful tool to engineer the dispersion of the light. Such structures, commonly known as meta-optics can achieve a non-trivial relation between the energy and momentum of photons. One particular possibility is to create a dispersion-free flat band, which allows a resonator to maintain the same resonance frequency for different incidence angles. In this work, we utilize a flat band meta-optic to create a photodiode which has a critically coupled absorption for a wide angular range (±18°). By implementing a lens-based concentrator, the size of the photodiode can remain small while collecting large amounts of light, which results in high resolution, low energy consumption, and fast operation speed of the photodiode.

Atomically thin materials enable the manipulation of light at the nanoscale, leveraging a diversity of polaritonic modes, from plasmons in thin metals and doped graphene to excitons in transition metal dichalcogenides and phonons in ionic insulators. We will discuss recent results on the fabrication and characterization of ultrathin noble metal plasmonic nanostructures, ultrafast carrier dynamics in those films, and advances toward complete coupling from plasmons in those structures to propagating light.

Meta-lenses, distinguished by their compact size and adaptable manipulation, have attracted considerable interest. Yet, challenges persist for conventional tunable meta-lenses, including complexity, high costs, and limited responses, constraining their performance and applications. In our research, we introduce innovative tunable water and 3D printing meta-lenses tailored for millimeter waves. This technology empowers the delivery of the focusing spot to arbitrary positions in two-dimensional or three-dimensional space. Notably, it allows the precise transmission of a highly concentrated signal to a specific location, with the added capability of adjusting the transmission direction freely. This breakthrough enables the development of secure, flexible, and highly directive 6G communication systems. Our proposed approach overcomes existing limitations and holds promise for diverse applications in wireless power transfer, zoom imaging, and remote sensing.

This talk introduces an on-chip realization of the discrete fractional Fourier transform (DFrFT), proposed and experimentally implemented in the microwave domain utilizing a passive metamaterial coupled lines network (MCLN). This renders a lensless device capable of performing the DFrFT in real-time. The MCLN comprises N microstrip transmission lines coupled to their nearest neighbors through an array of interdigital capacitors composed of interlaced microstrip fingers. In the latter, the dimension and number of fingers allow for controlled and enhanced coupling terms that render the required DFrFT couplings highly accurate. The MCLN is exploited to design a new compact planar electromagnetic lensless solution that enables a beam steering operation through the focal plane array concept. The latter is performed by independently exciting the input ports of the MCLN through a switch tree, while the output ports are connected to an antenna array to realize a focal plane array system. Contrary to other approaches, this device does not require any external phase element, reducing the overall power consumption.

Meta-optic commercialization and manufacturing readiness is an important topic as optics designers begin evaluating meta-surfaces into optics modules. Moxtek has established a volume production line for visible and NIR wavelength meta-optics with a manufacturing readiness level 8. This provides a unique environment to evaluate the uniformity and capabilities of meta-optic manufacturing techniques. With a statistically significant dataset, mild variations in design concept and lens characteristics can be easily highlighted. We will present baseline MTF and efficiency data related to a variety of metalens characteristics. The goal is to highlight unique meta-optic characteristics that impact performance in volume production. Moxtek has manufactured and characterized metalenses in a wide range of wavelengths, lens diameter, and focal lengths.

In this talk, I will discuss our recent progress on metasurfaces based on engineered nonlocalities, stemming from long-range resonant interactions and lattice phenomena locally perturbed through tailored symmetries. Engineered nonlocality in metasurfaces offers enhanced spectral control, both temporally and spatially, ideal for image processing, and enhanced light-matter interactions. We achieve these features by combining quasi-bound states in the continuum with geometric phase variations in engineered metasurfaces, tailoring at will the supported eigenwaves. The resulting metasurfaces support sharp responses selective to the impinging wave properties, effectively realizing ultrathin transparent films that highly reflect light only when illuminated by selected polarization, frequency and wavefront spatial distribution of choice. The demonstrated wavefront selectivity of nonlocal metasurfaces opens exciting opportunities for augmented reality, secure communications, thermal emission management, optical modulators and enhanced light-matter interactions for nonlinear and quantum optics. In particular, in the talk we demonstrate our recent experimental demonstrations on highly efficie

Controlling the quality (Q) factor and far-field polarization response of a metasurface is critical for many applications in classical and quantum optics with new applications driving the creation of increasingly sophisticated devices with multi-dimensional control. In particular, one emerging need is the ability to create and control nearly degenerate pairs of high-Q modes while robustly shaping the frequency splitting, Q-factors, and polarization responses across two bands simultaneously. Here, we solve this challenge with a design paradigm for pairwise control of symmetry-guaranteed pairs of symmetry-protected bound states in the continuum and their corresponding polarization singularities. We experimentally demonstrate dual band control over mode splitting, Q-factors, and polarization responses in dielectric metasurfaces. Building upon this demonstration, we will conclude by expanding the design methodology to enable narrowband wavefront shaping without deeply sub-wavelength features.

The high computational demand of deep neural networks for computer vision must be alleviated by hardware-based strategies to facilitate applications in resource constrained systems. A potential solutions is to offload computations onto a front-end analog optical preprocessor, which could perform low-level feature encoding operations instantaneously as images are captured. To that end, this study showcases incoherent, broadband, low-noise optical edge encoding for thermal imaging of real-world scenes, which is achieved using a hybrid system of a 24-mm, inversely-designed metasurface and a refractive lens. Using an inverse design approach, the metasurface is optimized for Laplacian-based edge detection across the 7.5 – 13.5 µm LWIR imaging band. This work could be expanded to enable optically-encoded feature maps for accelerating convolutional neural networks for image segmentation and classification.

Here, we introduce a novel demonstration of utilizing scalable nitride-based resonant plasmonic metasurfaces, with a work function of 4.7 eV, to dramatically augment the light-matter interaction in wafer-scale monolayer single-crystal MoS2 photodetectors. Our pioneering approach has achieved not only excellent responsivity but also an impressive detectivity of 2.58 × 1012 Jones via the plasmon-enhanced photogating effect. A salient feature of this work is the introduction of a novel concept: the giant photocurrent enhancement propelled by the local-electromagnetic-field enhanced photogating effect. This leads to a substantial 190-fold photocurrent boost compared to conventional MoS2 photodetectors.

Chirality, essential for distinguishing molecular enantiomers, impacts various scientific fields. Circular dichroism (CD) spectroscopy, which measures differential absorption of circularly polarized light, is limited by weak chiral-optical interactions, yielding minimal signals. Superchiral metasurfaces, enhancing optical chirality, offer improved CD signal and interaction with chiral molecules, necessitating advanced development for accurate analysis. This study presents a novel two-stage design methodology for optimizing superchiral metasurfaces, employing a neural network-based optimizer and adjoint topology optimization for enhanced optical chirality density. The results provide a platform for sensitive CD spectroscopy, facilitating fast optimization of metasurface unit cells for better chiral molecule analysis.

In this talk we will present our recent results related to metasurfaces. This includes new CMOS compatible platforms for structural colors, overcoming chromatic aberrations in metalenses, the fusion of atomic physics and metasurfaces, and metasurface real time control.

We report resonance gradient metasurfaces, which show nearly continuous tunability of the high-Q resonance over a broadband wavelength range. The spectral tuning of the high-Q resonance is realized by gradually scaling the unit cell’s geometrical parameters along one coordinate of the metasurface. By using the gradient metasurface and a tunable infrared laser, a resonantly enhanced tunable generation of optical harmonics over a broad spectral range is realized (Adv. Mater. 2024, 36, e2307494). Additionally, broadband biosensing and control of vibrational light-matter coupling by using the gradient metasurface were demonstrated. This research establishes the groundwork for innovative light-generating devices and biosensors.

We present nonlocal chiral metasurfaces with a relatively high-Q factor for the direct detection of Stokes parameters. To realize it, we leverage the optimized interaction between nonlocal and local resonances in a constituent nanostructured meta-unit. By revealing the working principles of such interaction, we experimentally demonstrate effective nonlocal resonance-based high-Q polarimetric detection, which affords the direct tracking of azimuthal and ellipticity paths at the Poincaré sphere. Such metasurfaces are demonstrated by designing nanostructured meta-units with minimal geometric perturbation from the circular nanopost and keeping the filling ratio of meta-units to be constant for all targeted Stokes metasurfaces. We further prove that such design approach ensures consistent sized nanofabrication and facilitates effective operation across different samples at specific wavelengths and polarizations in experimental setups.

We report on the active control of transmissive polarization switching of near infrared light in two dimensions (2D) using liquid crystal (LC) infiltrated Ti3O5 nanostructures with > 50% efficiency in experiment. Our device consists of a periodic array of elliptical Ti3O5 pillars submerged in a thin (~ 2 um) LC layer and supports overlapping electric and magnetic dipoles under linearly polarized incidence. Using a biased photoactive top contact, we manipulate light in 2D by patterning a 435 nm pump laser on its surface to locally modulate LCs in illuminated areas. This work can find applications in solid-state programmable beam shaping and steering.

With significant advances in mid-wave infrared (MWIR) photonics, reducing unwanted reflections is critical for MWIR devices. Recently, multi-resonant metasurfaces have emerged as a potentially attractive platform for broadband antireflection (AR) across the solar spectrum. Unfortunately, such metasurfaces provide only a restricted AR efficiency in a broader MWIR range. Here, we show that broadband AR can be enabled by leveraging the generalized Kerker effect on a judiciously designed elliptical Si metasurface. It is argued that the generalized Kerker effect can be maximized by suppressing the near-field coupling between Mie resonators and controlling the symmetry of resonators. With this understanding, we can achieve broadband AR with more freedom by engineering symmetry rather than physical dimensions. We demonstrate the value of our optimized metasurface by showing 1.9% averaged reflectance in the 2.5−6 μm spectral range. This work opens up new design strategies for antireflective nanophotonic structures applicable to high-performance MWIR devices.

Considerable demand exists for smart, low-cost and portable gas sensors. Although IR spectroscopy-based sensors work well for this application, their deployment is limited by their size and cost. We demonstrate a smart, low-cost, multi-gas sensing system comprising a mid-infrared microspectrometer and a machine learning algorithm. The microspectrometer is a metasurface filter array integrated with an IR camera. A machine learning algorithm is trained to analyze the data from the microspectrometer and predict the gases present. The system detects greenhouse gases carbon dioxide and methane at concentrations ranging from 10 - 100% with 100% accuracy. It also detects hazardous gases at low concentration levels with an accuracy of 98.4%. We detect ammonia at a concentration of 100 ppm. We detect methyl-ethyl-ketone at the permissible exposure limit (200 ppm). This work demonstrates the viability of using machine learning with IR spectrocopy to deliver a smart and low-cost multi-gas sensing platform.

Increasingly, we need to find and count channels for waves. In nanophotonics, knowing how many optical channels can usefully enter or leave a small structure is critical for understanding what the structure can do and how to design it efficiently. Though conventional diffraction theory gives useful answers for large objects, for nanostructure on wavelength scales, there has been no clear picture. We show how understand such channels based on a concept of tunneling escape of waves from small volumes. We also show how to find the best coupled channels automatically through arbitrary optics, based on self-configuring photonic integrated circuit processors, which function as real-time optical analog processing systems.

Using representation theory, one can prove that current implementations of symmetry-protected bound states in the continuum (BICs) in photonic crystal slabs can only yield BICs at the center of the Brillouin zone and below the Bragg diffraction limit, which fundamentally restricts their use to single- or few-frequency applications. Instead, this limitation must be overcome by altering the system’s radiative environment. In this talk, I will show how to create lines of BICs by altering the radiative environment surrounding a photonic slab, as well as degenerate pairs of symmetry-protected BICs with independent control over their Q factors and frequency splitting.

Photonic funnels, conical waveguides with hyperbolic metamaterial (HMM) cores, efficiently focus mid-IR light to spatial areas much smaller than the free space wavelength. These devices were originally conceived as having a perfect electric conductor (PEC) coating to confine light as it propagates to their subwavelength tip, however, recent numerical analysis demonstrates that funnels without a conductive cladding exhibit peak intensities over 1,000 times greater than their clad counterparts while maintaining a confinement scale determined by their tip radius. The funnel's conical surface provides an oblique interface between the highly anisotropic HMM and an isotropic medium. This oblique interface enables anomalous reflections which reshape and redirect the incident beam towards the funnel tip. In this work we analyze how the gold cladding suppresses the field enhancement and demonstrate the importance of the anomalous reflection to the funnel's performance.

Our study examines how light's angular momentum affects magnetic all-optical switching (AOS), which involves reversing magnetization using ultrafast laser pulses on a magnetic structure. The magnetic system consists of a ferromagnetic thin sheet of Co/Pt, which is stimulated by Femtosecond vortex beams of light can carry spin, orbital angular momentum, or both.

Large language models (LLMs) such as ChatGPT are trained on massive quantities of text parsed from the internet and have shown a remarkable ability to respond to complex prompts in a manner indistinguishable from humans. We present a fine-tuned LLM that can predict electromagnetic spectra over frequencies given a text prompt which only specifies the metasurface geometry. Results are compared to conventional machine learning approaches including feed-forward neural networks, random forest, linear regression, and K-nearest neighbor. We demonstrate the LLM’s ability to solve inverse problems by providing the geometry necessary to achieve a desired spectrum. Furthermore, our fine-tuned LLM excels at “physics” understanding, explaining how certain resonances are directly related to geometry. LLMs possess some advantages over humans that may give them benefits for research, including the ability to process enormous amounts of data, finding hidden patterns in data, and operating in higher dimensional spaces. We propose that fine-tuning LLMs on large datasets specific to a field allows them to grasp the nuances of that domain, making them valuable tools for research and analysis.

Strain engineering of the two-dimensional semiconductor gallium selenide has recently revealed exciting nanophotonic effects such as localized bandgap tuning, exciton funneling, and the creation of site-specific single photon emitters. We investigate the reversible local strain engineering of suspended gallium selenide flakes by using a novel micromechanical spring with nanoscale probes for inducing symmetry-controlled localized strain. By performing strain engineering measurements on suspended gallium selenide flakes as opposed to using patterned substrates, unintended strain originating from the surrounding environment is avoided. Our results show that gallium selenide undergoes a reversible bandgap redshift of >6 meV. The presented research establishes a new platform for streamlining the quantitative understanding of material properties as a function of complex local strain in two-dimensional materials for quantum photonics applications.

In this work, and inspired by the multimode fiber refractive index sensors, we propose and design a refractive index sensor in a silicon-on-insulator (SOI) semiconductor structure using a complex multimode resonator. The resonator is optimized with an adjoint-based inverse design topology optimization technique using the commercial software Lumerical. We model the structure in a two-dimensional platform and the device's effective refractive index is calculated based on a suitable figure of merit. The sensor is tailored to operate within the telecommunication band, making it suitable for applications such as wearable devices for patient monitoring or detection of pathogens or toxins in environmental monitoring. The biosensor's design is optimized for maximum sensitivity to changes in the surrounding refractive index within the 1450 nm to 1650 nm wavelength range. It is also compatible with standard fabrication processes and the minimum manufacturable feature size, which is crucial for practical implementation.

We present a dynamic metasurface driven by polarization-twisting beams to demonstrate the rotational Doppler effect. Polarization-twisting pulses, composed of left and right circularly polarized pulses with shifted center frequencies, generate a rapidly rotating linearly polarized field. We employed nanocylinders made of amorphous silicon as the building blocks of the metasurface. The rotating field alters the permittivity of the nanocylinders due to the nonlinear Kerr effect, thereby enabling the metasurface to function effectively as a fast-rotating waveplate. When a probe beam passes through this metasurface, both its frequency and spin state are altered due to the rotational Doppler effect. This phenomenon could be potentially used for developing magnetic field-free optical isolators.

Optical Rectification (OR), where photon frequencies subtract to give a zero-frequency direct current (d.c.), is an interesting nonlinear optical effect. Rectifying antenna-coupled diodes have produced the highest-efficiency microwave power conversion > 80%. Most IR detectors are expensive unsustainable semiconductors with a band gap, built n specialized clean rooms with trained staff, dangerous chemicals. Recently OR, not band gap limited, did not require an insulator or semiconductor; plasmonic metals are sufficient. We have observed a near-IR OR longitudinal current along the surface of a resonant 1-D metasurface (no photon drag), and coupling of incident photon helicity to plasmon transverse spin (“spin-momentum locking”). Future OR may be tuned. Here, we report experimental observations of OR voltages from off-center laser beam illumination and a transverse OR current (an ‘OR Hall Effect’), present in the same simple plasmonic gold film patterned into a 1-D grating; left-right patterning breaks symmetry. The strong stripe optical nonlinearity and field enhancement cross-couple higher order polarization terms generating a transverse OR current. We discuss applications.