We present experimental measurements of SHG and THG in the visible and UV ranges from crystalline silicon membranes 200nm to 2microns in thickness, and use the physical parameters retrieved to predict the properties of silicon metasurfaces. Our theoretical model predicts well both spectral and angular responses and efficiencies of the membranes. Silicon is centrosymmetric but possesses a third order nonlinearity that is dispersive and relatively large in the UV range. The results also suggest that judicious exploitation of the nonlinear dispersion of ordinary semiconductors has the potential to transform device physics well into the UV range.

This conference presentation was prepared for the Active Photonic Platforms (APP) 2022 conference at SPIE Optics + Photonics 2022.

This talk will review our recent studies on the nonlinear optical properties of conducting oxide epsilon-near-zero materials. I will present a method to engineer the field intensity enhancement of the Al-doped zinc oxide (AZO) ENZ thin films synthesized by atomic layer deposition technique. I will also discuss the observation of abnormal nonlinear temporal dynamic of hot electrons and enhanced optical nonlinearity in AZO and ITO ENZ thin films under different pump fluences and excitation angles using degenerate pump-probe spectroscopy and Z-scan nonlinearity measurement techniques. Our results on understanding the nonlinearity and ultrafast free carrier dynamics of ENZ materials will be important for efficient all-optical signal processing and nonlinear zero-index photonic applications.

Graphene plasmonics provides a powerful means to extend the reach of metasurface technology to the terahertz spectral range, with the distinct advantage of active tunability. However, most prior proposals of graphene THz plasmonic devices assume electrical characteristics that are not compatible with sufficiently large samples grown by chemical vapor deposition (CVD). Here we introduce a comprehensive design platform that can overcome this limitation, based on graphene nanoribbons combined with metallic antennas on a vertical cavity. With this configuration, we present a single device structure that can be electrically reconfigured to enable multiple wavefront-shaping functionalities, including tunable beam steering and focusing with variable numerical aperture. Applications of the same platform to THz light emission will also be discussed. These capabilities are promising for a significant impact in multiple THz technologies for sensing, imaging, and wireless communications.

We propose a graphene-based metamaterial for achieving tunable spectral absorptivity in the infrared. The metamaterial is modeled as a periodic array of electrically-tunable, coupled resonators. The structural parameters of the resonators are chosen to implement a dark-bright mode coupling scheme in the context of temporal coupled-mode theory. The spectral response of the metamaterial can be tuned from single-peaked to double-peaked absorption by tuning the resonance wavelengths of the constituent resonators relative to each other. Our results thus suggest the possibility of achieving tunable multi-band absorption using metamaterials composed of multiple coupled resonators.

We investigate strategies for designing metasurfaces with electrically reconfigurable infrared absorption and emission spectra. We use coupled-mode theory to provide a framework for design. One approach to tuning uses localized photonic resonators, while a second approach uses extended grating modes. We investigate the use of symmetry-breaking and period-doubling strategies to create, destroy, and shift spectral absorption lines. Such strategies are anticipated to be useful for the communication of information on multiple wavelength channels in the infrared.

A grand challenge for nanophotonics is the realization of tunable metasurfaces enabling active control of the key constitutive properties of light – amplitude, phase, wavevector and polarization. Active metasurfaces that enable dynamic modulation of reflection amplitude, phase and polarization have been recently explored using several active materials and modulation phenomena, including carrier index in plasmonic ENZ structures, reorientation of liquid crystal molecules, electrooptic effects in quantum well heterostructures and index change in phase change materials. The rapid advances in understanding of exciton resonances in layered van der Waals materials has now stimulated thinking about active metasurfaces that exploit excitonic modulation phenomena to enable ‘van der Waals active metasurfaces. As one example, I will describe recent advances in electrically reconfigurable polarization conversion across the telecommunication wavelength range in van der Waals layered materials, integrated in a Fabry-Pérot cavity. These results have broad implications for the use of monolayer materials in active metasurfaces, and I also will give a general outlook for the wide range of possibilities for active metasurfaces based on 2D material heterostructures.

The intrinsically strong and actively tunable light-matter interactions available in atomically-thin materials such as graphene and transition metal dichalcogenides offer dynamical control of near-field interactions, which can be utilized to manipulate their supported polaritons as well as quantum optical elements such as few-level fermionic systems. Here we discuss strategies to harness the electrically-tunable optical properties of 2D materials to interface with proximal quantum light emitters, mediate single-polariton-level nonlinear optical interactions on the nanoscale, and actively drive atomic systems into bistable states in integrated nanophotonic platforms.

Van der Waals materials are of great promise for photonics and optoelectronics. Here we discuss the use of high refractive index transition metal chalcogenides, such as MoS2, and hexagonal boron nitride for nanophotonics. We present our theoretical and experimental studies of a range of devices and components made of these materials, including waveguides, resonators, and metasurfaces. We demonstrate that these van der Waals materials allow extreme optical field confinement in deeply subwavelength structures. Our studies suggest that smaller and more efficient devices may be created with the use of van der Waals materials.

According to Fourier optics, the surface profile of an ideal diffraction grating should contain a precise sum of sinusoidal waves. However, because fabrication techniques typically yield profiles with only two depth levels, complex “wavy” surfaces cannot be obtained, limiting the straightforward design and implementation of sophisticated diffractive surfaces. Here, we eliminate this design–fabrication mismatch and produce optical surfaces with an arbitrary number of specified sinusoids, yielding previously unattainable diffractive surfaces including intricate two-dimensional moiré patterns, quasicrystals, and holograms. We then show that such patterns can be reduced to nanometer length scales, creating wavy Fourier surfaces for 2D electronics.

We will discuss recent advances in the design of applications based on the atomic-scale control of optical fields, including the use of atomically thin metals and semiconductors for enhancing the nonlinear response, achieving complete coupling of light into arbitrarily confined optical modes, and exploring quantum optics phenomena at unprecedentedly small length scales. Specifically, we will present our recent experimental and theoretical results on ultraconfined plasmons in few-atomic-layer crystalline silver films, complete optical coupling into plasmons and other types of surface polaritons though engineered optical scatterers, strong nonlinear response associated with two-dimensional metals and semiconductors, and their application to optical sensing.

In this talk I will cover our recent results tunable and strong light-matter interactions in van der Waals 2D and other low-dimensional semiconductors. I will first present our results on hybridized exciton-plasmon-polaritons in nanopatterned gratings of WS2. Following that I will present light-trapping and self-hybridized exciton-polariton formation in large area superlattices of WS2 and boron nitride. I will extend the results of self-hybridization to halide perovskites showing exciton-polariton emission at room temperatures and finally I will show the effects of cavity coupling and anti-ferromagnetic phase transition on tunable linear dichroism in van der Waals FePS3 semiconductor.

This conference presentation was prepared for the Active Photonic Platforms (APP) 2022 conference at SPIE Optics + Photonics 2022.

We propose a non-reciprocal infrared thermal emitter that exhibits unequal absorptivity and emissivity. Graphene grating over a slab is used to create high Q guided resonances. Dynamic modulation of Fermi energy of graphene is used to drive photonic transitions, inducing non-reciprocity. We show that strong contrast between absorptivity and emissivity can be obtained with realistic modulation frequencies of 10’s of GHz. This study presents a graphene-based platform for non-reciprocal thermal emitters.

In this talk, I discuss our recent research efforts on some new classes of time-varying metamaterial platforms, with a particular focus on (i) non-Hermitian time-varying media, and their application for broadband perfect absorption and one-way light propagation; (ii) drift-biased materials emulating moving media, which enable breaking temporal symmetries without the need for magneto-optical effects or complicated space-time modulations; and (iii) quantum electrodynamic effects in the presence of time-modulated electromagnetic environments. Our findings highlight the many opportunities offered by advanced time-varying platforms in electromagnetics and photonics.

Topological photonics enables unusual and robust properties of electromagnetic waves, including reflections-free photon propagation along strongly curved interfaces and localization at the corners and other discontinuities of photonic structures. Of particular interest are active topological devices whose properties can be changed on-demand. I will describe how graphene can become a platform for supporting topological polariton-excitons: new hybrid objects whose electronic and photonic properties can be actively controlled by electric gates. I will also discuss opportunities for using liquid crystals for developing topological and other tunable devices, such as varifocal lenses.

We report novel topological polaritonic states of half-light and half-phonon character in a topological mid-infrared metasurface integrating hexagonal boron nitride (hBN). A custom-built Fourier-space imaging microscope was used to investigate a three-dimensional band diagram of the photonic topological phonon-polaritonic states in our system for the first time. Our Fourier- and real-space imaging experimental findings, supported by theoretical models, demonstrate that topological properties of photonic modes are transcribed to the in-plane lattice vibrations (phonons) supported by hBN. As a result, the observed topological phonon-polaritons exhibit unidirectional propagation with the helical nature of vibrations and the resilience of the modes to sharp bends.

The WS2 monolayer encapsulated in two thin hBN layers was pumped at room temperature by a circularly polarized laser in order to excite one of the valleys (K or K’ valley). The refractivity spectra measured using both left- and right- CP probe with low intensity, revealed the nonreciprocal response at exciton resonance wavelength. Based on this effect, we propose a novel design of an isolator containing SiN ring resonator integrating an asymmetrically places WS2 monolayer. By applying the coupled mode theory and parameter extracted from the experiment, the isolation of the device was estimated to be ~20dB.

The recent development of 2D materials and photonic systems enabled the exploration of the twist degree of freedom. By adjusting the relative orientations of two adjacent layered structures, new phenomena such as Moire pattern enabled properties emerge, leading to unprecedented opportunities in tuning the light-matter interactions in both electronic materials and photonic systems. My group has been exploring the similarity and distinction between 2D electronic materials and their photonic counterparts. Here I’d like to introduce some of our recent findings that my group has made on the twisted degree of freedom in 2D systems, including the realization of controllable and continuous twist of 2D van der Waals materials and the exploration on the tunable optical response of the twisted van der Waals materials as well as the twisted photonic crystals.

I will present some of our recent results in the field of photonics, including novel phenomena in topology, and free electron sources of light.

Transmission symmetry is considered an inherent property of passive linear systems. It is believed that violating transmission symmetry would mean violating reciprocity which would require some active intervention, e.g., via an external magnetic field, or with time modulation or "non-linear self-biasing" of the system's optical components. Recent works though have shown that judiciously designed planar asymmetries at a linear passive structure's interfaces can cause polarization rotation and lead to transmission symmetry breaking without breaking reciprocity. Here, we present a linear and passive class of metagratings which preserve the polarization of the input beam but break transmission symmetry while still obeying reciprocity [1]. We analyze the underpinning mechanism and explain why it does not violate reciprocity. Breaking transmission symmetry with these simple systems can open-up several capabilities in integrated photonics from infrared to optical frequencies. [1] S. Foteinopoulou, Breaking Transmission Symmetry Without Breaking Reciprocity in Linear All-Dielectric Polarization-Preserving Metagratings, Phys. Rev. Applied 17, 024064 (2022); https://doi.org/10.1103/PhysRevApplied.17.024064

In topological photonic crystals, suitable crystal symmetries bring the concepts of topological insulators to nanoscale photonic components. We experimentally probe topological states in nanophotonic cavities and waveguides, and investigate to what extent light confinement, transport, and light-matter interactions can benefit from robustness offered by topological design paradigms. We show how the signatures of topological band structures are imprinted on the complex near and far fields of photonic crystal states, and how these can be used to control near-to-far field coupling. Using near-field investigation, we quantify the scattering of topological edge states at sharp corners and controlled disorder. Finally, we show that spin-orbit coupling in the near field of topological photonic crystals can become disconnected from the edge state pseudospin, important to the design of chiral light-matter interfaces.

Optical cavities and coupled resonators allow one to explore rich light-matter interactions including enhanced Purcell factors, exceptional points, quantum sensing and lasing. We discuss some recent developments of resonant mode theories for both passive and active resonators, connecting both classical and quantum mode theories in a quantitative way using quasinormal modes (QNMs). We show several applications of the theory, including a non-Hermitian coupled mode theory near exceptional points, a rigorous way to quantize QNMs for active-passive media, and chiral emission from linearly-polarized quantum emitters coupled to index-modulated ring resonators. We highlight several clear failures of the heuristic coupled mode theories.

Integrating machine learning into the inverse design, fabrication, and characterization of photonic devices brings computational speed-ups throughout the entire device design process. In this presentation, we report on using machine learning for improving the inverse design of nanophotonic meta-structures and speeding up the characterization of single-photon emitters under sparse measurements. We find that compressing the design space of meta-structures using autoencoders can greatly reduce the time required to compute high-efficiency designs using global optimization methods. With the characterization of single-photon emitters, we find that convolutional neural networks can classify the g2 correlation function of an emitter above or below the 0.5 correlation threshold up to 100 times faster than full characterization with 95% accuracy. Using this fast characterization of single-photon emitters, we can speed up super-resolution imaging up to 12 times faster than conventional methods. Our work paves the way for quantum machine learning-assisted global optimization of nanostructures and super-resolution imaging.

In a dynamically modulated ring resonator, the resonant modes at different frequencies couple together to form a lattice along the frequency axis. In this talk, we exploit such a lattice as a synthetic frequency dimension to explore novel non-Hermitian topological physics, and to perform optical computations.

The high demand for AI services in conjunction with a dramatic chip shortage along with technology leaps such as 5/6G networks, cybersecurity threats, and quantum algorithms have resurrected a R&D push for advanced information processing and computing capability. To address this demand and explore novel technology roadmaps, unique opportunities exist, for example, given by algorithmic parallelism of digital-analog hybrid non-van Neuman accelerators. Especially photonic-electronic ASIC compute paradigms hold promise to enable non-iterative O(1) runtime complexity, ps-short latency, and TOPS/W throughputs. This opens prospects for next-generation hardware both for AI cloud services but also for accelerating edge computing such as enabled by compact and efficient PIC-CMOS co-designs pushing the SWAP envelope. As both a professor and a co-founder of a deep-tech venture, in this seminar I will share my insights on fundamental complexity scaling and algorithm-hardware homomorphism on the one hand, and system-level synergies and co-design optimization strategies on the other. I will introduce a novel photonic RAM capable of zero-static power consumption suitable for edge applications and a mixed-signal tensor core accelerator leveraging parallelism. Beyond matrix-matrix multiplication acceleration, I will show how convolutions can be accelerated as simple dot-product multiplications in the Fourier domain and using display light technology enables 1000x1000 matrix convolutions at 100us latency, or about 10x faster than today’s GPUs. Finally, I will share latest opto-electronic device work such as 20Gbps ITO-based modulators that are 1,000x more compact than Silicon and LN modulators, and discuss scaling-length-theory slot-detectors featuring zero-bias detector and low NEPs.

As integrated photonics is seeing huge progress and renewed research interest, the focus on components that enable demonstrations of components such as tensor cores are becoming vitally important. In this talk I shall present recent progress on work in photonics that aims to enable some of the components required to effectively create on-chip active components for aspects related to computing (Feldmann et al, Nature, 2021; Li et al, IEDM 2020; Rios et al, Sci Adv 2019) as well as for emerging photonic signal processing applications.

The field of topological photonics leverages concepts from geometry and topology – the branch of mathematics that deals with global properties that cannot be changed under continuous deformation – to produce electromagnetic modes that propagate with immunity to certain types of disorder and imperfections. In the last few years, several experiments have achieved the generation and propagation of quantum states of light in these so-called topological modes, demonstrating enhanced robustness of such inherently fragile quantum states. In this talk we will focus on our recent results in this area including topological protection of spatial entanglement and the demonstration of topology as an additional degree of freedom for entanglement using CMOS-compatible silicon photonics platforms.

We report on the new metasurface-based and diffractive optical elements that help interface with two quantum systems: neutral atoms and color centers in diamond. These elements include diffractive elements that enable compact magneto-optical traps, metasurfaces that for efficiently generating optical bottle beams, and nanoscale structures to efficiently extract light from shallow color centers in diamond.

Our group recently discovered bright, stable, linearly polarized, and high-purity sources of single-photon emission at room temperature in SiN. Currently, we study the possibility of generating indistinguishable photons by plasmonic speed-up of photoemission, which may enable broader applications of SiN single-photon sources in quantum information technology. The enhancement of the light-matter interaction with plasmonic materials can shorten the spontaneous emission time to beat the dephasing time and achieve coherence even at non-cryogenic temperatures. Our findings spark further studies of quantum emitters toward deeper understanding of their nature, deterministic formation, and scalable integration with on-chip quantum photonic circuitry.

Plasmon antenna lattices enjoy a long history in the domain of fluorescence control, SERS, sensing and plasmon lasers, due to the combination of high Q and strong field enhancement, by virtue of diffractive resonances. Recent theory for honeycomb, Kagomé and distributed loss and gain lattices point at the potential for topological and pseudochiral bandstructure physics. For this regime, sub-diffractive periodicities are particularly interesting, pushing the array bandstructure beyond the light line and in a regime where plasmon antennas interact strongly. I will present experiments that access this band structure on basis of far-field reflective, fluorescence, and nonlinear Fourier microscopy.

Topology plays a fundamental role in contemporary physics and enables new information processing schemes and wave device physics with built-in robustness. Recently, significant efforts have been devoted to exploring topological principles in bosonic systems. In the first part of this talk, I will discuss my invention of topological lasers: integrable non-reciprocal coherent light sources as well as compact bound state in continuum sources. In the second part of the talk, I will discuss our recently proposed scheme to systematically implement singularities known as exceptional points (EP) in passive plasmonics. I will discuss the new scheme and how we overcame current immuno-assay nano sensing record with plasmons by more than two orders of magnitude. Finally, I will discuss how the topological phase around an EP singularity can be used to implement functional and multiplexed phased arrays, antennas, and metasurfaces.

The induction of synthetic magnetic fluxes allows to effectively control the localization and transport properties on a given lattice structure. In this work, we generate an effective magnetic flux where fundamental and first excited modes effectively interact. We implement a z-scan method on femtosecond laser written photonic lattices and experimentally observe Aharonov-Bohm caging, for both modes independently. We demonstrate a controlled dynamics where we perfectly translate the light across the lattice.

A new platform for miniaturized reconfigurable nanophotonics through integration of dielectric, semiconductor, and plasmonic materials with nonvolatile phase-change materials will be discussed. This platform enables reconfigurable photonic building blocks with subwavelength features. Important materials for operation in the visible and infrared wavelengths are discussed. Two groups of reconfigurable devices based on integrated photonic structures and metasurfaces along with their unique features for state-of-the-art applications will be covered. Design, fabrication, and potential applications of this platform for state-of-the-art devices and systems will also be covered.

Antimony trisulfide (Sb2S3) is an Earth abundant material that is transparent to visible and near infrared light (N-IR). Switching the material between amorphous and crystalline states causes radical property changes that deem it useful for programming the response of visible and N-IR photonics devices. We have demonstrated how Sb2S3 can be used to program high resolution micro-displays, dielectric metasurfaces, hyperbolic metamaterials, waveguides, and all-optical neural networks. This presentation will discuss these demonstrations and the underlying physics responsible for the phase transition in Sb2S3.

High-speed SLMs are necessary for various classical and quantum applications, including massively parallel remote sensing, high-repetition-rate pulsed laser shaping, and scalable control of quantum objects at timescales faster than their decoherence time. Here, we demonstrate a high-speed SLM by two-dimensional electric field patterning of a lithium niobate thin film. A high-quality factor guided mode resonance enhances the amplitude and phase modulation from the induced index variation. Our approach offers fast (> GHz), low power, and high diffraction efficiency tuning.

Lithium niobate (LN) has been the material of choice in optoelectronic technology due to its wide optical transparency (0.35–4.5 μm), large and robust electro-optic coefficients (r33 = 31.8 pm/V), and excellent chemical and mechanical stability. Recently developed nanophotonic electro-optic devices enabled the next-generation of electro-optic modulators featuring a significantly improved device performance regarding modulation efficiency, device footprint and bandwidth. We utilize plasmonic lithium niobate technology, where the metal electrodes guide both, surface plasmon polariton (SPP) modes and RF electric signals that control the optical properties of the supported SPPs, to demonstrate the most efficient and smallest lithium niobate modulator to date.

Metasurfaces are extremely versatile devices that offer wide control over the phase and amplitude of electromagnetic energy. However, their properties are often fixed at the time of fabrication. A critical challenge is to realize dynamically tunable metasurfaces, that are both fast and efficient. Applications such as telecommunications especially stand to benefit from metasurfaces with THz bandwidth. However, the large size of metasurfaces often limits their speeds to a few GHz. In this report, we demonstrate all optical tuning of a surface lattice resonance based plasmonic metasurface, that exhibits large Q-factors (>500), while providing 30x enhancement of pump beam absorption. This leads to over 150% modulation of the probe within the technologically relevant NIR window.

We provide insight into the operation and driving mechanism of an electro-optic spatial light modulator based on a Barium Titanate waveguide and an optically transparent electrode cladding layer. We employ electric field simulations, non-linear optics and techniques found in signal analysis to achieve sub-wavelength refractive index modulation of the waveguide. Our generic approach is applicable to Pockels and Kerr cells as well as liquid crystals and is capable of high-quality beam shaping and sensing. In this presentation, we focus on the operation of a reprogrammable Active Photonic Platform in the context of high-quality video holography.

Hydrogels such as PVA have yet to be fully exploited in metasurfaces due to their fairly low refractive index and fabrication feasibility. Here, we demonstrate one-step nanoimprinted PVA metasurfaces with resolutions reaching sub-100 nm, and aspect ratios approaching 10. We then demonstrate three distinct relative humidity dependent dual-mode optical security applications using the PVA metasurfaces. Through the swelling of the PVA when exposed to high humidity conditions and careful design of meta-atoms with different dimensions orientated at specific angles, multiplexed color prints and holograms can be selectively uncovered or destroyed.

We leverage the all-dielectric, essentially lossless, capabilities of a newly developed phase-change material by Y. Zhang et al. [1], GSS4T1, for dramatic light-path reconfigurability with a metagrating in the MWIR/LWIR spectrum (above 5 microns free-space wavelength) . We show that there are two entirely different governing physical regimes that control the metagrating responses, depending on the phase of GSS4T1, amorphous or crystalline. Specifically, we show that the proposed metagrating paradigm behaves as an effective metamaterial when GSS4T1 in the amorphous phase, while it supports leaky Floquet-Bloch waves when GSS4T1 is in the crystalline phase. These leaky Floquet-Bloch modes can exhibit accidental destructive and constructive interference into the zeroth and first-order Bragg transmitted beams respectively via a mechanism similar to the one responsible for the emergence of accidental bound states in continuum (BIC) phenomena. By utilizing these two different physical regimes, we demonstrate steering the incident beam to the negative direction when GSS4T1 is switched from the amorphous to the crystalline phase [2]. We believe these results are highly relevant to infrared devices and technologies such as long-range lidars, spectroscopic sensors etc. [1] Y. Zhang et al., Broadband transparent optical phase change materials for high-performance nonvolatile photonics, Nature Comm. 10, 4279 (2019). [2] N. L. Tsitsas and S. Foteinopoulou, Non-volatile MWIR/LWIR beam reconfigurability with all-dielectric metagratings comprising phase-change materials with a high-refractive-index shift, Opt. Mat. Express 12, pp. 3187-3212 (2022).

Active, dynamic, and reconfigurable control of photons and absorption is an important goal for many technologies. The ability to respond to, and be designed for, a wide range of wavelengths is critical and difficult for semiconductors. We discuss our recent discovery of optical ratchet rectification in an asymmetric plasmonic grating with no intrinsic chi(2) or nonlinearity, where direct (zero frequency) electrical current flows from incident photons ~4x larger than previous results. We report optoelectronic results on a metal-insulator-metal rectifier, reconfigured by rotating ferromagnetic moments in the top metal (Co), on Au/NbOx on Nb, Al. A magnetically-reconfigurable rectifier could be switched on and off with little energy, while retaining broadband response. Xanthommatin (Xa) is a small-molecule bio-pigment that can serve as a reconfigurable less-toxic photonic material.; we discuss actively controlling it using electromagnetic fields etc., presenting a model of the combined chromatophores and iridophores, a dynamically tunable photonic device in Nature.

I present recent results exploring the domain of multiple interactions in strongly scattering nanophotonic systems in the cross-over from effective medium to complex regime. We work along three main thrusts, which are firstly the fabrication of new materials with ‘extreme’ properties, secondly the precise characterisation of these materials using state of the art techniques (and in doing so push for the most extreme materials systems), and finally using these optimised materials in a series of completely new and original experiments in the nonlinear regime. Results presented here include new effective dielectric resonators obtained by micrometer-sized supercrystals synthesized using gold nanoparticle - DNA hybrids. We study the basic properties of these intriguing assemblies at the single nanocrystal level using spectral imaging. Second, we investigate the interactions in 2D oligomers of silicon Mie resonators in the presence of disorder to elucidate the effects of electric and magnetic dipole coupling and their sensitivity to disorder. Thirdly, we present investigations of ultrafast time dynamics in the light transport through complex media, giving rise to extraordinary nonlinearities mediated by multiple scattering.

All-optical magnetic switching represents a next-generation class of local magnetisation control, with wide-ranging technological implications. Existing all-optical switching schemes are unsuitable for device integration, typically requiring femtosecond-pulsed lasers and complex magnetic materials. Here, we demonstrate deterministic, all-optical magnetic switching using a low-power, linearly-polarised continuous-wave laser in nanoparticles with sub-diffraction limit dimensions composed permalloy. The poor absorption in permalloy nanoparticles is mitigated with an interference method to enable high fidelity magnetic writing at powers <3 mW. Isolated and densely-packed nanomagnets are switched. The results point to low-cost, low-power optically-controlled magnetic devices with impact across data storage, neuromorphic computation and reconfigurable magnonics.

The challenge for optical biosensors aimed at near patient testing is to achieve high performance at low cost, which includes the source and the readout instrumentation; this naturally requires trading off the various parameters of the system. We describe our sensor modality utilizing guided mode resonances, put it into context and discuss how this trade-off can be optimized for designing a viable device. We show how the technology can detect multiple markers for infection, combine the sensing and the spectrometer function in a single chip and achieve a limit of detection as low as 1pg/ml for common markers of infection. This performance is equivalent or better than laboratory-based techniques yet the sensor and instrumentation can be made entirely from low-cost components.

TIRF-Microscopy is widely used in cell biology to monitor dynamic biomolecular events occurring at the cell membranes. However, this technic is limited by weak fluorescence signal and background noise degrading the spatial resolution. We present high sensitive fluorescent TIRF-M using glass coverslips coated with one-dimensional photonic crystal (1DPC). The latter is made of dielectric multilayers optimized to generate a large field enhancement under TIR illumination at its free interface. Using a TIRF-microscope, we successfully demonstrate the capability of these substrates to enhance the fluorescence signal as compared to classical glass coverslips over fluorescently labeled HIV-1 and SARS-CoV-2 virus-like-particles imaging.

Integrated optics is an exciting platform to achieve optical measurement of T in the micro and nanoscale with high accuracy and reliability. Nevertheless, silicon microrings are affected by two-photon absorption (TPA) that limits the sensitivity of the devices because of self-heating. Wide-bandgap materials can overcome this problem. In this talk I will present some examples of the use of GaN and diamond-based microdisks that surpass the limits of silicon-based microrings. Also, silicon nitride nanomembranes have been used to obtain high-temperature resolution down to 15 K at room T.

Thermal radiation prompted the birth of quantum mechanics, and yet engineering thermal radiation has mostly remained in the classical realm. Quantum description of thermal light sources requires non-Hermitian description. Here, we develop a non-Hermitian description of nanoscale thermal emitters and demonstrate them using hybrid plasmonic and photonic metasurfaces. Our work shows that phase, symmetry, and topology, the new design tools offered by the quantum treatment relax the trade-offs between various performance parameters. We show selective thermal emitters with an emitter efficiency >80%. Such extreme-engineered nanophotonic devices alone enable applications such as flexible thermophotovoltaic energy conversion and we demonstrate it.

Using exceptional point dynamics in time and space modulated lattices we propose a new mechanism for generation of asymmetric robust higher harmonics. Specifically we design a metallic-silicon system with a complex optical potential spatiotemporally modulated along the length of the waveguide for this robust higher harmonic generation. In our system the dynamical equations associated with modal field amplitudes are described by a Jordan form Hamiltonian. This ultimately will allow for a unidirectional higher frequency generation which always has a maximum value for a specific length of the waveguide irrespective of the geometrical imperfections in the design of the waveguide. Furthermore, the phase of the generated higher harmonic mode becomes independent of the coupling between the fundamental frequency and higher harmonic one. Unlike other proposed spatiotemporal modulated systems when the system has a Jordan form Hamiltonian, the fundamental mode remains reciprocal while the harmonic generation is non-reciprocal. Consequently, while the proposed device cannot be used as an optical isolator it can be used for many other devices such as laser cavities, interferometry, and holographic processes.

We will discuss two kinds of exceptional points of degeneracy in waveguides and their respective application in lasers. Such exceptional points occur in waveguides with balanced loss and gain (e.g., PT symmetry), and in waveguides without loss and gain (e.g., periodic Si waveguides). Waveguides with such exceptional points have a strong degeneracy of their wavenumbers and polarization states that enables specific wave physics, only found in these degenerate systems. We will discuss advantages and disadvantages of both concepts to conceive laser regimes, related to high power, high spectral purity, high efficiency, etc, and show some realistic designs involving Si ridge waveguides.

We report the design and fabrication of a PT-symmetric coupled-cavity AlGaAs MQW laser for THz beat frequency generation. The optical source consists of two PT-symmetric coupled-cavity resonators and an amplifying waveguide section, producing a beat frequency in the THz band. When the beat frequency is fed into a photomixing cell, a coherent THz signal is produced. The THz frequency can be tuned by varying the gain contrast between the two individual resonators.

A new approach for engineering the controllable asymmetric coupling in active cavity lattices is experimentally demonstrated. Non-Hermitian skin effect is observed in the proposed Hatano-Nelson phase-locked laser array along with single mode lasing and variable emission distribution. The freedom to design at will the exchange interactions in active lattices enables many possibilities in optics, ranging from a new class of reconfigurable lasers capable of generating steerable emission, to non-Hermitian topological lattices.

Bound states in the continuum (BICs) emerge throughout Physics as leaky/resonant modes that remain, however, highly localized[1]. They have attracted much attention in Photonics, and especially in metasurfaces[2,3]. One of their most outstanding features is their divergent Q-factors, indeed arbitrarily large upon approaching the BIC condition (quasi-BICs) [4,5]. Here we investigate how to tune quasi-BICs in magneto-optic (MO) all-dielectric metasurfaces. The impact of the applied magnetic field in the BIC parameter space is revealed for a metasurface consisting of Si spheres with MO response. Through our coupled electric/magnetic dipole formulation, the MO activity is found to manifest itself through the interference of the (MO-induced) out-of-plane electric/magnetic dipole resonances with the in-plane magnetic/electric (directly induced) dipole, leading to a rich, magnetically-tuned quasi-BIC phenomenology, resembling the behavior of Brewster quasi-BICs for tilted vertical-dipole resonant metasurfaces. Such resemblance underlies our proposed design for a fast MO switch of a Brewster quasi-BIC by simply reversing the driving magnetic field. This MO-active BIC behavior is further confirmed in the optical regime for a realistic YIG nanodisk metasurface through numerical calculations. Our results present various mechanisms to magneto-optically manipulate BICs and quasi-BICs, which could be exploited throughout the electromagnetic spectrum with applications in lasing, filtering, and sensing [6]. References [1] Chia Wei Hsu, et al., Nat. Rev. Mater. 1 16048, (2016) [2] D.C. Marinica, et al., Phys. Rev. Lett., 100, 183902 (2008) [3] Chia Wei Hsu, et al., Nature 499, 188 (2013) [4] Kirill Koshelev, et al., Phys. Rev. Lett. 121, 193903 (2018) [5] Diego R. Abujetas, et al., Sci. Rep. 9, 16048 (2019) [6] Diego.R. Abujetas, et al., Nanophotonics 10, 4223 (2021)

We develop the theory of the crystallization phenomena for charged interlayer excitons (CIE) discovered recently in highly excited transition-metal-dichalcogenide (TMD) heterobilayers. We derive the ratio of the average potential interaction energy to the average kinetic energy and discuss the ’cold’ long-range crystallization phase transition for the many-particle CIE system in the absence and in the presence of a perpendicular magnetostatic field. In the zero-magnetic-field case, the strongly correlated phases are predicted — crystal and Wigner crystal for the unlike-charge and like-charge CIEs, respectively, — that can be selectively realized with TMD bilayers of properly chosen electron-hole effective masses by just varying their interlayer separation distance. In the non-zero-magnetic-field case, we generalize the effective g-factor concept previously formulated for interlayer excitons to include the formation of CIEs. We show that magnetic-field-induced Wigner crystallization and melting of CIEs can be observed in strong-field magneto-photoluminescence experiments with TMD heterobilayes of systematically varied electron-hole doping concentrations. Our results extend the potential capabilities of the TMD bilayer heterostructures, and can be used for coherent photon emission control, charge transport and spinoptronics application development with this new family of transdimensional quantum materials.

By coupling near-infrared electromagnetic and MHz-frequency flexural resonances one can dramatically enhance the magnitude of actuation and optical response in dynamically reconfigurable nanostructures. We review recent work on metamaterials driven by ponderomotive optical forces at microwatt power levels and by low-intensity acoustic vibrations, which manifest strong opto-mechanical nonlinearity, asymmetry and bistability.

Recently several attempts by using transfer printing method for integration of on-chip laser into silicon circuit. These approaches can minimize wasted III-V areas but has the disadvantage of requiring high alignment tolerances. Here, we propose a new concept of hybrid silicon laser, which is high tolerable in alignment. Employing the whispering gallery mode laser in conjunction with III-V patch layer, designed hybrid micro-patch laser has high design flexibility, and lower the process difficulty in fabrication. We expect the hybrid micro-patch laser to be the next generation device of on-chip micro-lasers.