This PDF file contains the front matter associated with SPIE Proceedings Volume 11461 including the Title Page, Copyright information, and Table of Contents.

For device applications, structural disorder and optical scattering have long been considered annoying and detrimental features that were best avoided or minimized. In this talk, I will show that disorder and complexity can be harnessed for photonic applications, in particular, to provide unique functionalities of photonic devices. We recently developed an on-chip random spectrometer that combines high resolution with small footprint. In addition, we incorporated disorder to a laser to reduce the spatial coherence for free-speckle full-field imaging, and to disrupt coherent nonlinear coupling of lasing modes to suppress temporal instabilities.

Welcome to the Active Photonic Platforms XII conference

2D materials have a number of intriguing value proposition that could be harnessed for compact, tunable, high-performance optoelectronic devices when heterogeneously integrated in photonic circuits. Here I review our latest work including; (1) tunable TMD-based microring resonator with engineered critical-coupling condition, (2) a broadband graphene plasmon-slot detector (R=0.7A/W), (3) a bandgap-shifted strain-engineered absorption-enhanced MoTe₂ photodetector at 1.55um (R=0.5A/W, low-dark-current <10nA@-1V), (4) a record-high responsivity (R=1.4A/W) slot-plasmon exciton-modulated MoTe₂ detector, (5) a MoS₂ electro-absorption modulator all enabled by our recently developed method of cross-contamination-free yet deterministic dry transfer 2D material ‘printer’ mimicking a 3D printer for enabling rapid prototyping. These devices are based on heterogeneous integration of 2D materials into Silicon and SiN photonics, with the latter used for on-exciton modulation or exciton absorption.

Under adequate illumination of plane wave, polarizable nanoparticles near a plasmonic surface acquire out-of-plane polarization spin and experience lateral forces thanks to the recoil of directional surface plasmons excited on the surface. The strength and direction of such forces are mostly controlled by the power and direction of the incoming light. Here, we show that illuminating a nanoparticle near a drift-biased graphene metasurface excites unidirectional surface plasmons whose trajectory is fully determined by the drift-current and does not depend on the direction of incoming light. Due to momentum conservation, unidirectional lateral forces are exerted on the particle with a strength that can be controlled and even amplified over two orders of magnitude by the applied DC bias. Our findings may resolve delicate laser beam alignment issues and reduce the beam intensity required for the trapping and routing of nanoparticles.

Active metasurfaces have received remarkable attention due to the advantage of adjusting their functions without changing physical structures. However, the previous active metasurfaces suffer from an inevitable correlation between amplitude and phase modulation of light. They inherently lack the degrees of freedom to independently control the amplitude and phase of light due to their single resonant design. We introduce a metamolecule which incorporates two consecutive graphene plasmonic nano-resonators. The metasurface using active metamolecules can be free from correlation problems and independently control the amplitude and phase of the scattered wave. A generalized graphical approach has been developed for an intuitive design guideline. Furthermore, dynamic beam steering and holographic wavefront reconstruction are demonstrated by full-wave simulation.

We employ Phase-Change Materials (PCMs) for local addressing of individual meta-atoms in both metallic and low-loss dielectric metasurfaces. PCMs provide a switchable dielectric environment for resonant nanostructures, altering their resonance frequencies in a non-volatile, reversible way. Specifically, we introduce a new tunable all-dielectric IR Huygens’ metasurface consisting of multi-layer Ge disk meta-units with strategically incorporated non-volatile PCM and demonstrate the optical programming with single meta-unit precision using hyperspectral measurements.[1] We also introduce a new programmable nanophotonics platform based on the next-generation “plasmonic” PCM In3Sb1Te2 (IST). [1] A. Leitis, A. Heßler, et al. Advanced Functional Materials, accepted (2020).

Here we present a novel concept and its optimization of multi-level quantized non-volatile photonic memories based on a compact hybrid phase-change-material GSST-silicon Mach Zehnder modulator, with low insertion losses to serve as node in a photonic neural network. We demonstrate a 3-bit (8-state) photonic nonvolatile memory heterogeneously integrated into silicon PICs. We show switching operation of this device from the crystalline to the amorphous state using thermal heaters on-chip. We then show how these photonic memory elements can be utilized to design and demonstrate photonic tensor core functionality in vector matrix multiplication (VMM) engines with a compelling runtime complexity of O(1) uses O(N^3) resources (devices) could perform in the range 2-500fJ/MAC, 1-50 TMACs/mm^2, and ~100ps (1 clock cycle) per VMM operation.

Phase change photonics has become a promising research field due to its applications in non-volatile photonic memory, optical switching, signal processing, and neuromorphic photonic computing. Absorption tunability in phase change materials enables weight setting with fast speed, low power consumption, and multilevel operation for matrix multiplication with high dimensions. Applying wavelength division multiplexing scheme can largely enhance the computation capacity in a broadband manner. In this talk, we shall review our recent progress in photonic memory and neuromorphic devices using different switching methods.

The recent development of fabrication techniques and material platforms allows addressing various multi-constrained problems in many areas including on-chip circuitry, imaging, sensing, energy, and quantum information technology. However, these require advanced design development methods, which can go beyond conventional optimization. We will discuss recent and promising advances in the development of photonic components based on topology optimization. One of the main aspects of current work is expanding and streamlining a conventional meta-device design methodology to a global optimization space. Specifically, we will cover our recent efforts on coupling topology optimization techniques with deep generative algorithms for dielectric/plasmonic metastructure design development.

Design in a proper way, optical dielectric resonant multilayers can support huge optical field enhancement when working under total internal reflection. TIRFM - Total Internal Reflection Fluorescence Microscopy, also based on total internal reflection illumination, is used in cell biology imaging where many biological processes involve cell membranes and their immediate intracellular spatial environment (signaling, cellular traffic, adhesion...). We propose to develop an enhanced version of TIRFM by investigating the optimization, conception and implementation of dedicated optical dielectric resonant multilayers as the glass coverslip replacement. Model samples such as lipid bilayers with a known thickness will be first investigated but our ultimate goal is to image more complex biological processes such as viral budding, or molecular transport mechanisms such as exocytosis or endocytosis.

So-called ‘iridoplasts’ found in certain species of the genus Begonia are alike to common chloroplasts found in most plants, but with a modified, periodic internal structure reminiscent of a 1D photonic crystal. Modelling indicates that this structure gives the Begonias their iridescent blue leaves, while also enhancing the absorption of photosynthetically active radiation. We will present an overview of the nano-optical theory underlying the model of iridoplasts, contrasting the design goals and constraints of biological and artificial systems. We use a simplified optical model based on Lorentz oscillators to answer the question of if the measured structure parameters of the iridoplasts are photonically optimised or if they reflect other biological constraints. Our results show that optimised photonic absorbers will not necessarily have high reflectance, raising the possibility that photonic structures for light harvesting in nature are more common than previously believed.

We derive upper bounds to free-space concentration of electromagnetic waves, mapping out the limits to maximum intensity for any spot size and optical beam-shaping device. For sub-diffraction-limited optical beams, our bounds suggest the possibility for orders-of-magnitude intensity enhancements compared to existing demonstrations, and we use inverse design to discover metasurfaces operating near these new limits. We also demonstrate that our bounds may surprisingly describe maximum concentration defined by a wide variety of metrics. Our bounds require no assumptions about symmetry, scalar waves, or weak scattering, instead relying primarily on the transformation of a quadratic program via orthogonal-projection methods. The bounds and inverse-designed structures presented here can be useful for applications from imaging to 3D printing.

In the last decades, designs of most incandescent sources have been realized by heating the whole device. Here we propose a novel approach consisting in taking advantage of hot nanoemitters that can be cooled in a few tens of nanoseconds. It offers a new opportunity for high speed modulation and for enhanced agility in the active control of polarization, direction and wavelength of emission. To compensate the weak thermal emission of isolated nanoemitters, we propose to insert them in some complex environments, such as e.g. the gap of cold nanoantenna, which allow a significant thermal emission enhancement of the hot nanovolume. In order to optimize this kind of device, a fully vectorial upper bound for the thermal emission of a hot nanoparticle in a cold environment is derived. This criterion is very general since it is equivalent to an absorption cross-section upper bound for the nanoparticle. Moreover, it is an intrinsic characteristic of the environment regardless of the nanoparticle, so it allows to decouple the design of the environment from the one of the hot nanovolume. It thus provides a good figure of merit to compare the ability of different systems to enhance thermal emission of hot nanoemitters.

Quantum mechanics states that quantum fields are never at rest but constantly fluctuate even at zero temperature. These fluctuations lead to extraordinary physical consequences such as spontaneous emission and Hawking radiation. In this talk, we show experimentally that quantum fluctuations of electromagnetic field can induce phonon coupling between nearby objects and thus transfer heat across a vacuum. We use nanomechanical systems to realize strong Casimir phonon coupling, and observe thermal energy exchange between individual phonon modes by monitoring their thermal Brownian motions. Our experiment reveals a new mechanism of heat transfer in addition to the conventional conduction, convection and thermal radiation. It opens up new opportunities to study nanoscale energy transport and quantum thermal dynamics.

Here, we show that magneto-optically resonant particles present a large anisotropic thermal magnetoresistance (ATMR) in the near-field radiative heat transfer when the direction of an external magnetic field is changed with respect to the heat current direction. We illustrate this effect with the case of two InSb particles where we find that the ATMR amplitude can reach values of up to 800% for a magnetic field of 5 T, orders of magnitude larger than its spintronic analogue. We also show that this two InSb particles experience non-reciprocal forces leading to a Stern-Gerlach like effect and permanent non-reciprocal torque.

Past work in infrared meta materials has demonstrated the ability to tune the thermal emissivity of a material in the spectral domain. Much of this work has been based on single resonant modes. Here, we explore the new capabilities provided by systems of multiple, coupled resonators for emissivity tuning. In particular, we demonstrate how coupling can be used to enhanced tenability and reconfigurability for the cases of structural and index tuning.

Silicon photonics is considered to be the leading platform to achieve faster data transfer speeds on-chip. However, the weak electro-optic coefficient of silicon limits the maximum achievable data rates. A hybrid solution consisting of a silicon photonic backbone and an incorporated optical phase change material (O-PCM) that provides improved optical functionality may provide the solution for realizing broadband, low power, small footprint on-chip photonic devices capable of achieving record modulation speed. In this presentation, we discuss theoretical and experimental work integrating O-PCMs in silicon photonic devices, including sub-picosecond optical switching using a hybrid silicon-vanadium dioxide waveguide.

Optical metasurfaces, planar sub-wavelength nano-antenna arrays with the singular ability to sculpt wave front in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel functionalities. A particularly intriguing research direction within this field is active metasurfaces, whose optical response can be dynamically tuned post-fabrication, thus allowing a plurality of applications unattainable with traditional bulk optics. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning covering the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles. We implement the approach to realize a high-performance varifocal metalens. The metalens is constructed using Ge₂Sb₂Se₄Te₁ (GSST), an O-PCM with a large refractive index contrast and unique broadband low-loss characteristics in both amorphous and crystalline states. The reconfigurable metalens features focusing efficiencies above 20% at both states for linearly polarized light and a record large switching contrast ratio (CR) close to 30 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents the first experimental demonstration of a non-mechanical active metalens with diffraction-limited performance.

The phase transition in vanadium dioxide (VO2) has been widely studied for applications in electronics and photonics. This talk will describe the optical properties of VO2 from the visible to the far-infrared ranges, and present tunable devices that utilize the phase transition in this material, including tunable absorbers, optical filters, thermal emitters, optical limiters, and limiting diodes.

Actively tunable optical materials integrated with engineered subwavelength structures could enable a new generation of optoelectronic devices with low power consumption for on-chip hyperspectral focal plane arrays or optical beam steering. Phase-change materials, such as vanadium dioxide (VO2), are a promising solid-state solution for dynamic tuning; however, previous demonstrations have focused on VO2 films with >50 nm thickness, limiting their use in e.g. optical memory devices. Here we integrate nanometer-thick VO2 films with plasmonic metasurfaces to demonstrate tunable near-perfect absorption in the near-IR ranging from 900 nm to >1500 nm. Upon heating to induce the phase transition, the absorption resonance can be blue-shifted by up to 40 nm, a process that can be completely reversed by cooling and repeated over multiple cycles. Finite-element simulations follow the experimental spectral dependence and demonstrate that ~160 nm of tuning may be possible with further optimization.

Dielectric and semiconductor meta-surfaces offer the potential to construct high-efficiency, compact optical components through nanoscale patterning. There currently is substantial interest in developing dynamically reconfigurable and switchable meta-structures, such that the behavior can be tuned in real-time. In this work, we experimentally demonstrate electrically and thermally tunable meta-structures that utilize metal-insulator phase transitions. We demonstrate 1) switching between dielectric and plasmonic resonances in VO2 Mie resonators and 2) electrically-controlled, continuous, broadband tuning of infrared reflection and absorption in hybrid Ge-VO2 structures.

In this talk, we present our latest research progress in the area of non-reciprocal and topological photonics based on nonlinearities and external pumping with optical fields. We show that it is possible to largely break reciprocity and induce Faraday rotation, non-reciprocal polarization conversion, non-reciprocal phase shifts, isolation and circulation by externally pumping suitably designed nonlinear optical resonators. Realistic implementations based on silicon photonic ring resonators and optomechanical systems will be presented and discussed, with a vision for practical realizations in the context of quantum photonics and computing.

In this talk, we theoretically and experimentally investigate intriguing optical properties of non-Hermitian coupled nanoresonators based on two dimensional photonic crystals. Firstly, we demonstrate that a one dimensional array of PT symmetric coupled nanoresonators exhibits exotic optical dispersion near the exceptional point (EP). Second, we demonstrate that a similar non-Hermitian coupled resonators having equal coupling strength exhibits a topological insulating phase when we appropriately pump specific resonators. This system is unique because we can create the topological insulating phase from a homogeneous resonator chain only by manipulating gain and loss with a certain order, leading to reconfigurable optical non-trivial topology. Thirdly, we show our recent experimental demonstration of the PT phase transition in non-Hermitian coupled resonators based on electrically pumped photonic crystal nanolasers. The result shows an interesting enhancement in the vicinity of EP.

The landmark discovery of photonic topological insulators has opened a unique route for disorder-immune light transport with unprecedented possibilities of practical applications. Flexible reconfiguration of topological light pathways can enable a completely new paradigm for high-density photonics routing, sustaining the growing demand for data capacity. By strategically interfacing non-Hermitian and topological physics, we demonstrate arbitrary robust light steering in reconfigurable non-Hermitian junctions, where novel chiral non-Hermitian topological states can propagate at an interface of the gain and loss domains. In contrast to previously studied topological states confined only at the static boundary/interface of the structure, the new non-Hermitian-controlled topological state can enable robust transmission links of light inside the bulk, fully utilizing the entire footprint of a photonic topological insulator.

We report on nonlinear eigenmode and scattering properties of lattice resonances in 2D plasmonic antenna arrays and metasurfaces coupled to spatially distributed loss and gain. Dispersive lattice resonances have already been used to realize plasmon antenna array lasers. Here we go beyond lasers and homogeneously distributed gain. We report on band structures of plasmon lattices with spatially distributed loss and gain, where we show under which conditions topological features related to PT-symmetry occur despite the fact that plasmon arrays are very far from usual tight-binding descriptions, due to dominant far-field retarded interactions. Our experimental work includes first results in which we spatially program gain and loss by shaping of pump light incident on the arrays, and ultrafast response properties probed by two-photon luminescence and interferometric autocorrelation generated in the metasurfaces.

Light-matter interactions in photonic nanostructures including microcavities, waveguides, plasmonics, and quantum dot emitters opens a wide range of exciting optical regimes, with applications ranging from quantum light sources to sensing and low-threshold lasers. This talk will describe some recent developments in the efficient modelling of these complex optical systems, covering a range of topics, including long-range disorder effects in slow-light photonic crystal waveguides, intrinsic losses in topological edge states, and quantized quasinormal modes for understanding quantum optics in plasmonic systems and cavity-QED. All the theoretical approaches exploit intuitive mode theories, combining the benefits of physical intuition with efficient modelling techniques.

We introduce the recently emerged field of all-dielectric resonant metaphotonics aiming at the manipulation of strong optically-induced electric and magnetic Mie-type resonances in dielectric and semiconductor nanostructures with relatively high refractive index. Unique advantages of dielectric resonant nanostructures over their metallic counterparts are low dissipative losses and the enhancement of both electric and magnetic fields that provide competitive alternatives for plasmonic structures including optical nanoantennas, efficient biosensors, passive and active metasurfaces, and functional metadevices. This talk will summarize the recent advances in nonlinear, topological, and active metaphotonics. In particular, we demonstrate nanophotonic topological cavities hosting semiconductor quantum wells, and observe room-temperature lasing with narrow spectrum, high coherence, and threshold behavior. We also discuss the recent progress with optical bound states in the continuum.

Topological photonics aims to utilize topological photonic bands and corresponding edge modes to implement robust light manipulation. Importantly, topological photonics provide an ideal platform to study nonlinear interactions. In this talk, I will review some recent results regarding nonlinear interactions of one-way edge-modes in frequency mixing processes in topological photonic nanostructures. More specifically, I will discuss the band topology of 2D photonic crystals with hexagonal symmetry and demonstrate that SHG and THG can be implemented via one-way edge modes. Moreover, I will demonstrate that more exotic phenomena, such as slow-light enhancement of nonlinear interactions and harmonic generation upon interaction of backward-propagating edge modes can also be realized. Finally, FWM of topological plasmon modes of graphene plasmonic crystals and SHG upon interaction of valley-Hall topological modes of all-dielectric photonic crystals will be discussed.

The concept of synthetic dimension allows one to explore higher-dimensional physics in lower-dimensional physical systems that are easier to implement experimentally. We discuss some of our recent efforts, where we use the dynamic modulation of refractive indices to explore various topological photonic concepts in synthetic dimensions.

After a successful decade of purely fundamental research, the topological photonics community is starting to explore applications more seriously. Among the most promising fields of application for topological photonics are integrated laser sources and quantum circuits. In this talk I will review the latest results on topologically protected quantum states of light, with an emphasis on our recent experimental demonstration of topological protection of photonic path entanglement. Our experimental platform is a bipartite lattice of silicon nanowires which supports to uncoupled topological edge states. By using a common weak pump evenly split between the two edge modes, and leveraging four-wave mixing in the silicon nanowires, we were able to encode a biphoton N00N state of two topological edge modes. We demonstrate that this spatial entanglement is preserved even in the presence of deliberately induced disorder in the position of the waveguides.

A quantum state, such as a qubit state, defined in a parameter space is endowed with a property called the geometrical property. The geometrical property tells how much the quantum state changes in a parameter space; this property is a gauge invariant, physical, quantity, but it has not been experimentally observed until very recently. We give a simple experimental protocol to measure the geometrical property by periodically modulating the system and looking at the system response. The method can be easily applied to various qubit systems such as diamond NV centers and superconducting qubits. We will also review the current experimental situations regarding the measurement of geometrical structures.

Indistinguishable and/or entangled photons propagating in waveguide arrays (WAs) represent a promising platform whose utility ranges from research on fundamental aspects of quantum mechanics all the way to applications in quantum sensing and quantum information processing. Quantum simulators of decoherence reveal that while decoherence processes inevitably destroy single-particle coherence and any form of multiparticle entanglement, quantum correlations based on particle indistinguishability do endure. Further, by judiciously combining multi-photon states with the idea of synthetic dimensions in WAs yields the notion of a synthetic atom and in turn this provides entirely novel perspectives on the dynamics of such multi-photon states. Similarly, simple beam splitters fed with indistinguishable photons, can be used to perform discrete fractional Fourier transforms or can be tuned to realize exceptional points of any order. The latter setup facilitates efficient quantum-enhanced sensors.

Topological states of light can be induced in nanophotonic systems by encoding spin or valley degrees of freedom in the electromagnetic vector field. We study topological light propagation and storage in waveguides and cavities in two-dimensional photonic crystals at telecom wavelengths, directly imaging their propagation and band structure in experiment. Through phase- and polarization-resolved measurement of the states' electromagnetic fields, we reveal their origin in photonic spin-orbit coupling. Our quantitative measurement techniques allow us to test the level of topological protection in these systems, which rely on spatial symmetries to achieve topological robustnes. We study topological protection of backreflection at sharp corners and defects and discuss the merits of these principles in realistic nanophotonic devices.

Materials with nontrivial topological properties may also be found in standard optical systems like photonic crystals and waveguide arrays. Many of these systems are characterized by a well-defined topological winding number (also known as the Brouwer degree). We pick several interesting optical model systems to show that the winding number is a very simple topological concept, which can often be guessed intuitively. However, even for minor modifications of the standard topological model systems the use of the simplest types of winding numbers is no longer justified. Thus, we also present ongoing research to employ other intuitive topological concepts.

Two anisotropic exceptional points (EPs) of arbitrarily high order are found in a class of random non-Hermitian systems, where the non-Hermiticity emerges from non-reciprocal hoppings. Both eigenvalues and phase rigidity show different asymptotic forms near the anisotropic EP in two orthogonal directions in the parameter space, making them anisotropic EPs. The critical exponents of phase rigidity follow universal rules near an anisotropic EP, and the exponents depend on the dimension of the Hamiltonian as well as the approaching direction, but are independent of the random configurations. We found multiple ellipses formed by EPs of order two converge to the two high-order EPs in the parameter space. A ring of high-order EPs is formed when all ellipses coalesce for some particular configurations.

The purpose of this paper is to examine the behavior of exceptional points (EPs) in a time delayed anti-parity-time symmetric system composed of two delay-coupled semiconductor lasers (SCLs). Starting from a pseudo-2x2 rate equation model for the lasers’ electric fields we analyze the eigenvalues and eigenvectors of the system’s effective Hamiltonian and numerically search for EPs. Recent experimental work has suggested that the EP landscape in this system may be significantly different from the typical anti-PT dimer due to the time delay. Exceptional points in these PT dimers mark global phase changes from overall oscillatory behaviour to exponential growth/decay; in contrast, the time delay renders our effective Hamiltonian infinite-dimensional and allows for more than one EP. Specifically, we numerically demonstrate that by tuning the delay time or coupling strength our time delayed system may exhibit one, two, or zero EPs.

One of the most notable property of non-Hermitian systems is the emergence of spectral degeneracies known as exceptional points where complex eigenvalues and the corresponding eigenstates of the system coalesce. The presence of an exceptional point affects the system’s behavior significantly, leading to nontrivial physics with interesting features. In this talk, I will present the progress in our experimental and theoretical studies towards a better understanding of the control of light and its interaction with matter at exceptional points for realizing photonic and phononic devices with novel functionalities.

Slow-light has enriched many intriguing optics phenomena in which nonlinearities and gain/absorption among other features can be significantly enhanced. We link the concepts of slow light and exceptional points of degeneracy (EPDs) and discuss the relation with PT-symmetry. They emerge in coupled waveguides when multiple eigenmodes coalesce in both their eigenvalues (wavenumbers) and eigenvectors (polarizations), when varying a specific system parameter, like coupling, dimension, frequency, etc. The number of eigenmodes that coalesce at the EPD determines the order of the EPD. For example, in lossless structures, the regular band edge (RBE), the stationary inflection point (SIP), and degenerate band edge (DBE); are 2nd, 3rd, and 4th order EPDs, respectively. We explore the existence of various orders of EPDs in mainly two types of periodic coupled waveguides: the modified coupled resonators optical waveguide (CROW) and in coupled dielectric slabs with multiple gratings. The formulation is based on coupled mode theory and it can be generally applied to several other periodic structures. The existence of EPDs in optical structures provide unique properties like the giant scaling of the quality factor and high density of states and these two can also be made independent of each other. The unique properties of EPDs make it possible to induce single-frequency lasing just by introducing a small level of gain. Guiding periodic systems with EPD exhibit unprecedented scaling of the lasing threshold. Such scaling in a N-unit cells periodic structure follows new physical scaling laws as a function of the order of the EPD. We show an example of CROW based on Silicon-on-insulator (SOI) technology and report the lasing action in such configuration using the finite-different time domain (FDTD).

I will provide an overview of the field, with special emphasis on the photonic emulation of the canonical quantum topological phases such as the Hall, spin-Hall, and valley-Hall phases, as well as higher-order topological phases. I will also discuss how the ideas from topological photonics can be used for complete reimagining of the architectures of photonic devices such as add/drop filters, delay lines, and logical gates based on the valley degree of freedom of photons (“photonic valleytronics”). Finally, I will discuss the prospects of realizing reconfigurable topological photonic structures on a nanoscale. The prospects for exciting topologically protected microwaves using high current beams, and using the latter for high-power magnets-free microwave radiation, will also be discussed.

Topological phases have raised great interest in the photonics community. So far, most studies follow the theoretical framework established in electronic systems, and focus on linear optical systems. In this talk, I will discuss some of our recent progress in achieving topological phases in driven nonlinear optical systems and their potential applications.

Topological excitations in photonic crystals and metamaterials can be observed in many different guises. While passive periodic structures can support essentially topological Bloch modes, the insertion of quantum degrees of freedom can lead to a wealth of topological solutions such as solitons and vortices. We will present a survey of recent results in the field and try to describe the transition between trivial and non-trivial phases by studying the phase space of these structures.

Higher-order topological insulators (HOTIs), originating from quantized quadrupole and octupole moments, have attracted significant interest since they support boundary states that are two or more dimensions lower than their bulk. However, previous HOTIs have been restricted to real-space dimensions. Here we construct photonic HOTIs using synthetic dimensions, comprising frequency modes of dynamically modulated rings. We show how quadrupole and octupole HOTIs supporting topologically protected corner modes emerge in a lattice of modulated photonic molecules and predict a dynamical topological phase transition in this system. Additionally, we propose a quantized hexadecapole (16-pole) insulator by leveraging synthetic dimensions to create a 4D hypercubic lattice that cannot be realized in real space.

In this work we design and experimentally realize a photonic kagome metasurface exhibiting a Wannier-type higher-order topological phase. We demonstrate and visualize the emergence of a topological transition and opening of a Dirac cone by directly exciting the bulk modes of the HOTI metasurface via solid-state immersion spectroscopy. The open nature of the metasurface is then utilized to directly image topological boundary states. We show that, while the domain walls host 1D edge states, their bending induces 0D higher-order topological modes confined to the corners. The demonstrated metasurface hosting topological boundary modes of different dimensionality paves the way to a new generation of universal and resilient optical devices which can controllably scatter, trap and guide optical fields in a robust way.

Localized emitters in atomically thin 2D materials and lateral heterostructures are of interest for flexible optoelectronic and nanoscale quantum applications. We investigate near-field photoluminescence (PL) and Raman signals of local heterogeneities such as nanobubbles, lateral heterostructures and alloys in monolayer and few-layer transition metal dichalcogenides coupled via polariton-like surface waves and plasmon-enhanced hot electrons. We investigate various emitter coupling schemes and near-field enhancement mechanisms and demonstrate near-field imaging of exciton funnels, revealing a strong synergistic enhancement of the PL signals due to the plasmonic antenna tip, hot electron injection, and exciton funnelling. This opens new avenues in exploration of novel nanophotonic coupling schemes.

In this talk, we will focus on the subject of strong light-matter coupling in excitonic 2D semiconductors. We will present our recent work on the fundamental physics of light trapping in multi-layer TMDCs when coupled to plasmonic substrates. We systematically demonstrate via calculations and matching experiments that the presence of strong excitonic resonances in multilayers (< 20 nm thickness) combined with surface plasmon excitations of the nearby metals can achieve strongly coupled modes with apparent voided crossings in reflectance spectra. Further, we explore additional light confinement by patterning 1D arrays of rectangular resonators of varying widths and periods (100 nm to 500 nm) showing three mode couplings. We will further present extensions of our studies to resonators with dielectric spaces and optical superlattices in 1D.

Plasmonic transdimensional materials offer advances such as thickness-controlled light-matter coupling and novel space-time symmetry breaking phenomena to further develop the fields of nanophotonics and optical metasurfaces. Much is unclear though about their optical response and quantum near-field effects. We use quantum electrodynamics and a confinement-induced nonlocal dielectric response model to study the epsilon-near-zero modes of metallic films in the transdimensional regime. New remarkable effects are revealed such as the plasmon mode degeneracy lifting and the dipole emitter coupling to the split epsilon-near-zero modes, leading to thickness-controlled dipolar spontaneous emission with up to three-orders-of-magnitude increased rates.

In order to design high Purcell-factor systems, hybrid cavity-antenna systems have shown to be highly promising. We show in what way a system of a high-Q cavity combined with a low-V antenna can outperform its constituents, and give rules of thumb for their design for several applications. In particular, we will present experimental results of different hybrid systems including microdisk resonators and integrated photonic crystal nanobeams coupled to rod and dimer antennas respectively. By placing single quantum dots, we experimentally measure the high Purcell factors these systems promise.

We report on experiments where high-Q silicon nitride microdisks couple to arrays of plasmon antennas. Such hybrids promise `best of both world’ performances, i.e., subwavelength mode volume yet high Q, with exciting repercussions for spontaneous emission control, sensing, and plasmon-enhanced Raman scattering. In this framework it is particularly interesting to understand antenna-antenna interactions mediated through a resonant cavity. In a first experiment we examine cooperative dipole-dipole coupling of antenna dimers coupled through a whispering gallery mode, and demonstrate implications for high-Purcell factors with `chiral’, properties, i.e., unidirectional circulation. In a second experiment we studied far-field OAM generation by rings of antennas on cavities, demonstrating simultaneous pure OAM and pure polarization control through unit-cell design. Finally we report on the potential of such structures for molecular optomechanics.

Plasmon-based lasers and surface plasmon amplified spontaneous emission of radiation devices (spasers) have garnered significant attention since their prediction over a decade ago. Major advances have included subwavelength footprint sizes, room-temperature operation, far-field emission directionality, and understanding of the lasing mechanism. Notably, one simple architectural design for the plasmonic lasing cavity, nanoparticle lattices, has emerged as a powerful platform to achieve exquisite control over the coherent light. This talk will describe how tuning of the lattice symmetry and nanoparticle characteristics as well as the type of gain material can result in fine control over the wavelength, threshold, angle of emission direction, and polarization of the nano-lasing signals.

Strongly coupled exciton-polariton systems enable the miniaturization and integration of photonic circuits. They represent, for instance, ideal building blocks for the fabrication of low-threshold micrometer-size lasers. In this work, we demonstrate the achievement of an electrically controlled laser in strongly coupled exciton-polariton GaAs/AlGaAs planar waveguides. We introduce an additional degree of freedom in the lasing frequency by applying an electric field through the heterostructure, which allows to switch in real time between different Fabry-Pérot modes. Our system enables the realization of multiple micrometer-size electrically controllable lasers, thus making it suitable for the construction of polaritonic optical circuits and coherent light sources.

In this article, we present experimental and simulation results of a novel dual-wavelength laser source that emits in the regime of 764nm and 820nm. These wavelength regimes are chosen to match the absorption lines of oxygen gas and water vapour. The dual-wavelength laser source is realised by combining two External Cavity (EC) lasers on a SiN platform. In particular, each of these EC lasers is formed by butt-coupling a SiN resonant mirror to a reflecting semiconductor gain chip that results in highly monochromatic source (10MHz) to match the narrow absorption lines of the gases. Ultimately, this SiN based dual-wavelength source will have applications in the field of biomedical for continuous monitoring of oxygen in body cavities.

Low-loss plasmonic materials offer unique opportunities for quantum information applications. A strongly targeted enhancement of light-matter interaction can be used to speed up spontaneous emission of single photons by solid-state defects by several orders of magnitude, even at room temperature. We have developed several methods for the on-chip integration of such plasmon-enhanced single-photon sources. We also present some applications of plasmonic materials for the active control of solid-state spins. In the future, integrated plasmon-enhanced devices can be used as a platform for cryogen-free high-speed integrated quantum photonics.

Atoms with narrow-line resonances play a major role in high precision measurements like magnetometry and atomic clocks. Due to their long inherent coherence time, atoms can serve as quantum memories as well. Moreover, as they possess well-defined electronic levels, coherent interactions with the photon fields can be used to manipulate their quantum states very precisely. Besides, the capability of the optical excitation and read out, increase the spatial resolution of the atomic sensors. Within the last couple of decades interfacing atoms with engineered confined light fields has been a proper playground for investigating various quantum-electrodynamical effects. So far different strategies have been utilized successfully to integrate atoms with a confined light field, for example in high-finesse optical cavities, hollow core fibers, and tapered nanofibers. While cold atom setups provide ideal conditions and controllability to explore different coupling regimes, the large setups required to cool and trap the atoms have hindered their scalability for any realistic quantum networks. Thermal vapors, on the other hand, allow for less precision and control, but their low technical complexity and suitable compatibility with miniaturization and integration make them a promising candidate for realizing scalable networks.

In this work, we study transient THz conductivity of tungsten diselenide (WSe2) thin films to assess its potential for high-speed THz modulators, i.e., with pulsed optical excitation one could potentially realize all-optical, terahertz devices. Time-resolved THz spectroscopy, across different samples, reveal carrier recombination lifetimes of ~10-100 ps and a transient conductivity that exhibits a non-Drude behavior. We observe a strong dependence of the photoconductivity on the grain size. Based on this study, we can provide a general framework to understand the interplay between grain size and transient conductivity and leverage its role for ultrafast modulator design in terahertz metamaterials.

Lithium niobate (LN) has been the material of choice for electro-optic modulation due to its wide optical transparency (0.35–4.5 μm), large electro-optic coefficients (r33 = 30 pm/V), which are preserved at elevated temperatures due to its high Curie temperature (~1200°C), and excellent chemical and mechanical stability resulting in long-term material reliability. However, combining this attractive material platform with plasmonics is largely unexplored. Here, we demonstrate monolithic and compact plasmonic modulators based on the Pockels effects in LN, where the metal electrodes utilized for applying a RF electric field inherently supports the propagation of the modulated surface plasmon polariton modes. Extreme confinement and good spatial overlap of both slow-plasmon modes and electrostatic fields allow us to demonstrate record high electro-optic efficiencies for modulator devices based on LN

All-optical switching of metasurfaces enables dynamic control of the amplitude, phase and the polarization of light at picosecond timescales. The large free-carrier induced permittivity changes in transparent conducting oxides enable all-optical switching at femtosecond to picosecond timescales in planar, unpatterned films, without the need for lithography. In this work, we experimentally demonstrate the wide-tuning of the optical properties of three materials to achieve fast optical switching with large modulation depth. Lithography-free designs such as Fabry-Perot cavities, metal-dielectric mirrors, and Berreman-type metasurfaces are demonstrated to showcase optical switching at powers on the order of 1 mJ/cm2. The switching speeds can vary from 50 ps in cadmium oxide, 20 ps in ZnO to 2 ps in aluminum-doped zinc oxides. Our work will pave the way to practical optical switching spanning the telecom to the mid-infrared wavelength regimes.

Data usage across the internet is growing exponentially, fueled primarily by the move to cloud computing and penetration of streaming services into developing countries. To address the growing energy needs of data centers, we propose an all oxide plasmon assisted electro-optic modulator, which features enhanced light-matter interaction, and compact sizes as seen in plasmonic modulators while at the same time maintaining low insertion losses, as seen in photonic modulators. This is achieved by utilizing a device design that selectively engages and disengages the lossy plasmonic component, as the device switches from low transmission to high transmission modes.

The next-generation technology poised to revolutionize our society is 3D displays, and tunable nanophotonics is the key. Tunability in optical devices has been achieved in the past by many techniques including electrical doping, chemical doping, mechanical actuation, and optical nonlinearity. However, they all present either fast and small or slow and large tuning response. An unconventional material that can exhibit a large tuning with MHz response is 1T-tantalum disulfide. We observed unity order refractive index change in the visible at room temperature with an in-plane DC bias, AC bias, and moderately intense white light illumination (2.5 Suns). The strong correlations in this material give rise to charge ordering even at room temperatures and result in the large tunability. Using this new optical material, we demonstrate tunable meta-devices operating in the visible.

Materials with switchable optical characteristics can enable new types of optical technology that can be tuned or reprogrammed after fabrication. Here, I will present recent results on controlling light on a chip using tunable and programmable materials. New perturbative concepts for altering the flow of light in silicon integrated photonic circuits were initially developed in our lab through ultrafast photomodulation of the silicon waveguide itself. Implementation of reprogrammable photonics using the perturbation approach are now made possible by integrating phase change materials onto the silicon photonics platform. In particular I will be presenting the first results on a new family of new low-loss phase change materials for reconfigurable nanophotonic devices.

Due to their small physical footprint, fibre integrated metamaterials and metadevices made from phase change chalcogenide semiconductors that can be dynamically reconfigured using optical or electrical stimuli present the most promising platform for integration into future telecommunication networks to alleviate the data latency and high power consumption associated with current network configurations. Here, through numerical simulations, we present reconfigurable metadevices that can be integrated onto the tip and side of commercial optical fibres showing tunable behavior across the entire telecommunication band. Such devices can be used for dynamic dispersion control and signal switching.

In this abstract, I will discuss our efforts in realizing active thin film color filters and stimuli-responsive dynamic metaholograms for advanced display applications. Firstly, as a proof of concept for carrier concentration-controlled tunable device, we propose a tunable all solid-state color filter based on indium gallium zinc oxide (IGZO) active layer in a metal/dielectric/IGZO/metal cavity structure. By modulating the carrier concentration of IGZO, a resonance peak from the structure can be shifted around 50 nm in visible. Secondly, the stimuli-responsive metaholograms with designer liquid crystal will be discussed. To realize electrically tunable or other external stimuli (heat and surface pressure)-reactive metahologram, we adopt the functionalized liquid crystal in the spin-encoded metahologram. This kind of approach will may open up new emerging applications such as hologram mark for food safety (such as beverage freshness over temperature) and tangible holographic displays.

We present theoretical and experimental advances on photon-pair generation through spontaneous parametric down-conversion (SPDC) in nonlinear nanostructures and metasurfaces, underpinning quantum entanglement engineering at sub-wavelength scale for photon shaping with tailored polarization and spatial correlations. We derive explicit theoretical expressions for the measurable photon counts and quantum correlations, incorporating material dispersion and absorption characteristics [Phys. Rev. Lett. 117, 123901 (2016)], and demonstrate experimentally the generation of quantum heralded photon pairs from a single AlGaAs nanodisk [Optica 6, 1416 (2019)]. We further reveal the opportunities to enhance the generation rate through high-Q resonances including bound states in the continuum [doi:10.1117/12.2539888 (2019)]. We also outline the applications of metasurfaces for the manipulation and measurement of multi-photon quantum states for free-space quantum imaging and communications.

Effects of extreme nonlinear optics, such as high harmonic generation (HHG), are conventionally modeled with classical electromagnetic fields: both the driving and emitted fields are treated classically. We present the fully quantum electrodynamical theory of extreme nonlinear optics and use it to predict new quantum effects in HHG. The quantum description shows new effects in both the spectral and statistical properties of HHG. We also describe how the HHG process changes in the single-atom regime and discuss experiments that can test our various predictions. Revealing the quantum-optical nature of HHG could lead to novel sources of attosecond light having intrinsically quantum statistics, such as squeezing and entanglement.

The use of semiconductors such as GaAs, GaP or Si in the process of fabrication of actual nano devices is at the front edge of nowadays technology, exploiting the properties of light propagation and localization at nanometric scale in new and surprising ways. At these scales the usual theory describing the nonlinear effects of electromagnetic fields are pushed to the limit of usual approximations and should be revisited and analyzed. Recently, we have studied in detail the generation of the second and third harmonic the opaque region of GaAs and Si, going beyond the previous studies and deeply analyzing the nonlinear process in order to infer which are the different mechanisms leading to the second and third harmonic generation at the surface of these materials. We demonstrate that the bulk nonlinearity is not the only one active term and that we have strong contributions coming from the surface and magnetic Lorentz terms, which usually are either hidden by the bulk contributions or assumed to be negligible. Experimental and theoretical simulations are contrasted, using a hydrodynamic model [1,2] that accounts for all salient aspects of the dynamics, including surface and bulk generated harmonic components. [3] The study, made in detail for GaAs is extended here to other semiconductors as Si and GaP. We also consider resonant structures as gratings and nanowires capable to strongly enhance the nonlinear efficiencies. Although the harmonic generation in this regime and materials still has low efficiency, these findings have significant repercussions and are consequential in nanoscale systems, which are usually investigated using only dispersion less bulk nonlinearities, with near-complete disregard of surface and magnetic contributions and their microscopic origins.

Second-order optical processes are pivotal to the active modulation and wave mixing of light waves. The inversion symmetry in most materials, however, prevents achieving a bulk chi-2 effect, thereby limiting the portfolio of second-order nonlinear materials. We propose and demonstrate ultrafast conversion of a statically-passive dielectric to a transient second-order nonlinear medium upon the generation and transfer of plasmonically induced hot electrons. Triggered by an optical switching signal, the amorphous dielectric with vanishing intrinsic chi-2 develops dynamically tunable second-order nonlinear responses, which can be leveraged to address the critical need for all-optical control of second-order nonlinearities in nanophotonic systems.

Although recent advances in metamaterials and metasurfaces have dramatically extended their capabilities, the impact and applicability of such engineered materials is still hindered by several physical limitations and bounds, especially in relation to bandwidth and size restrictions. Lately the notion of dynamic spatio-temporal modulation of material properties has been the subject of growing interest and research efforts, opening a new landscape of opportunities, and providing new means to go beyond various conventional limits in photonic systems. Here, we provide an overview of our recent work on overcoming the bandwidth restrictions for open resonators, scatterers, and metasurfaces. We also discuss the exciting possibility of enabling novel, anomalous, nonlinear wave dynamics through judicious modulation of material properties in both space and time.

Integrated photonic nanostructures provide powerful degrees of design freedom for the engineering of light confinement and advanced lightwave manipulation functions. The ability to tailor field profiles in these on-chip devices allows enhanced light-matter interaction, strong modal confinement and the ability to engineer dispersion. Here, we present recent developments in photonic integrated circuits towards the generation of solitons, amplification, and optical waveform manipulation. By harnessing CMOS platforms with a high nonlinear figure of merit, the existence of on-chip Bragg solitons, Bragg soliton fission and solitons in photonic waveguides are experimentally observed. These demonstrations are made possible by 1,000X larger dispersion close to the band edge in on-chip Bragg gratings, an effect that arises from the interaction of forward and backward propagating fields. In addition, efficient parametric processes facilitate wavelength conversion of light and high gain amplification of signals. These efficient nonlinear mechanisms provide a possible pathway in which to realize new approaches to efficiently manipulate optical waveforms.

Since the invention of the laser, nonlinear optical phenomena have been a cornerstone of photonics research empowering advances in both continuous and pulsed lasers, molecular spectroscopy, and sub-diffraction imaging others. Although many nonlinear media have been explored through the years, ever more compact and efficient platforms remain a key driver in the field. Recently epsilon-near-zero (ENZ) materials, media with a spectral range where|Re{ε}| < 1, have emerged as a compact and versatile approach to enhance various nonlinear processes such as refractive index tuning, harmonic generation, and phase conjugation. In this talk, we discuss the unique underlying conditions that make ENZ materials a promising nonlinear platform and employ a framework of carrier kinetics to describe the nonlinear effects in Drude-based ENZ materials such as the transparent conducting oxides (TCOs). Through this approach, we focus on the large and ultrafast reflection and transmission modulation in TCOs enabled by the intensity-dependent refractive index, highlighting general trends as well as optimal material and excitation conditions. In particular, the role of absorption and non-parabolicity of the energy bands are discussed, culminating in a general figure of merit for comparing the performance of new potential ENZ materials. Finally, we describe recent advances utilizing the ultrafast refractive index tuning to generate an adiabatic frequency shift of a probe beam’s spectrum.

Highly-doped graphene has emerged as a promising material platform for nonlinear plasmonics that combines long-lived and electrically-tunable plasmons with an intensely anharmonic response to light originating from its unique electronic band structure. Here the appealing nonlinear optical properties of graphene are demonstrated to persist in its nanostructured form, even down to molecular sizes, where plasmons supported by significantly fewer electrons than those of noble metal nanoparticles are found to exhibit intense harmonic generation and extraordinary thermo-optical switching capabilities. Nonlinear plasmons in graphene nanostructures are further shown to undergo strong coupling with nearby quantum emitters or amongst themselves, potentially enabling nonlinear interactions of plasmons on the single-photon level.

The alloying of metals (Ag, Au, Cu, Al) has enabled the development of optical materials with unprecedented permittivity values, not found in its pure counterparts. Specifically, we overcome the constrain imposed by the pre-defined permittivity of pure metals by demonstrating the unique near- and far-field optical properties of these alloys for energy harvesting devices, and how they are correlated with the alloys band structure. Moreover, we demonstrate superabsorbers using Al-Cu/semiconductor with near-unity (>99%) and omnidirectional absorption in the visible and NIR range of the spectrum, formed by a simple dual-layer thin film stack. Concerning reconfigurability, we present a platform for transient photonic devices based exclusively on earth-abundant materials: Mg and MgO. We show color pixels covering the entire sRGB, where the hues can vanish in a few minutes upon system's exposure to water, very relevant for applications ranging from encryption to biodegradable displays.

Harnessing the unprecedented spatiotemporal resolution capability of light to detect electrophysiological signals has been the goal of neuroscientists for nearly 50 years. Yet, progress towards that goal remains elusive due to lack of electro-optic translators that can efficiently convert bioelectronic signals to high photon-count optical signals. Here, we introduce an ultrasensitive and extremely bright field-effect active plasmonic nanoantenna translating tiny electric field oscillations to large optical signals in the far-field. Our electrochromically loaded plasmonic nanoprobes overcome the limitation of state-of-art neuroelectrode technologies and enable massively multiplexed measurement of nanoscale electric-field modulations. In our experiments, we demonstrated 500 million parallel, ultrasensitive and subcellular resolution recordings of cell firing behavior, reflecting a technical capability that is well beyond the theoretical limits of the state-of-art neurotechnologies.

The important nonlinear effect of optical rectification in active metasurfaces,converts high frequency vis/infrared light to direct current. Recently, researchers discovered a reconfigurable optically rectifying junction. We focus on 3 junctions: 1) optical rectification in a simple, lithographically-defined Metal-Insulator-Metal (MIM) diode consisting of a planar Al electrode, a thin Al₂O₃ barrier layer, and a planar Ag counter-electrode. Applying a voltage grows nm-scale filament from the Al side. 2) nanoplatelet and substrate that demonstrates single-electron tunneling (SET) predict and model low-energy (< fJ) and high speed (>MHz) synaptic operations 3) Experiments conducted to determine whether a ferromagnetic layer in MIM reoriented can change the direct current and the rectified current, when exposed to an incident laser beam. This large tunability enables adaptive ultrafast photon detectors, wireless power transmission, energy harvesting, advanced antennas, computing.

We present a detailed investigation of a novel platform for integration of spintronic memory elements and a photonic network, for future ultrafast and energy-efficient memory. We designed and fabricated magnetic tunnel junction (MTJ) structures based on (Tb/Co)x5 multilayer stack with optically switchable magnetization. Optical single-pulse measurements allowed us to estimate the value of the stray field present in the parallel configuration, which prevents the structure from all-optical switching. We performed numerical calculations based on the Finite Difference Time Domain method and ellipsometry measurements of (Tb/Co)_x5 to compute the absorption by the MTJ structure. Simulation results are in good agreement with the experimental measurements, where we implemented a thermal model to estimate effective absorption in the pillar. These estimations showed up to 14% absorption of the incident optical power in 300-nm-wide MTJ. Moreover, we designed and realized an integrated optical network with focusing structures to efficiently guide and couple the light into the MTJs. We show a chain of necessary steps to obtain the threshold value of the switching energy, and our results presenting a path forward for full system integration of optically switchable MRAM technology.

We present the experimental observation of photon-photon interactions at the single-particle level. The linearly polarized signal beam undergoes Faraday rotation by a nonlinear effective magnetic field induced by a very weak circularly polarized control beam due to the giant Kerr-like interactions between exciton-polaritons in our quantum well-based 0D microcavity structures. We measure a phase shift with a slope of 3.5×10^-3 radians per particle for low cavity occupancies between 0.1 and 3 excited by the control beam. These experimental findings are in agreement with theoretical models and pave the way towards the development of scalable photonic quantum gates.

In this talk, we present our recent work on passive or active manipulation of the polarization state of light with both 2D and 3D metastructures. First, we illustrate an approach to tune efficiently the phase difference of light in two orthogonal directions by controlling the time retardation with a microstructured surface. Second, we demonstrate the general mechanism to construct the dispersion-free metastructure, in which the intrinsic dispersion of the metallic structures is perfectly cancelled out by the thickness-dependent dispersion of the dielectric spacing layer. Third, we present a freely tunable polarization rotator for broadband terahertz waves using a metastructure, and also an example on dynamically switching the polarization state of light based on the phase transition of vanadium dioxide. The investigations provide some guidelines to control the polarization state of light at subwavelength scale.

Direct printing of semiconductor nanoparticles via laser-induced transfer is a recently developed tool to obtain individual nanoparticles or their arbitrary arrays on a substrate of almost any shape and material. Semiconductor nanoparticles supporting Mie resonance are now widely explored in the pursuit for the novel all-dielectric photonic platforms. The promising direction is merging Mie-resonant nanoparticles with photonic crystals. We experimentally demonstrate excitation of a Bloch surface wave in photonic crystal mediated by an individual silicon nanoparticle. The nanoparticle being irradiated by light with the wavelength near the Mie resonance acts as a nanoantenna and allows excitation of the Bloch surface wave from the far-field. Visualization of the surface wave propagation direction is performed by the Fourier-plane imaging using the leakage radiation microscopy setup. We show that tuning the wavelength of the incident light around the Mie resonance allows for launching Bloch surface wave in both forward and backward direction.

Plasmonic nanolasers have excellent potential for ultrafast modulation due to their ability to accelerate spontaneous emission and increase the modulation bandwidth. Critical metrics of the nanolaser dynamics include photon lifetime, spontaneous emission rate, and polarization lifetime. However, these processes have significantly different lifetimes, which presents a challenge for modeling. Classical rate equations fail to predict the modulation behavior accurately. In this talk, we cover some history of the numerical modeling of nanoscale lasers and discuss our efforts on developing accurate computational approaches to describing modulated plasmonic nanolasers. We also highlight the regimes where multi-scale methods can still be used efficiently.

We show strong coupling of a mid-infrared microscale resonator with ultra-localised plasmonic nanocavity modes. This enables new types of mixing between IR absorption and surface-enhanced Raman scattering (SERS), opening up new types of ultrasensitive molecular detection. Nanoscale localized optical cavities are self-assembled by depositing Au nanoparticles onto few μm metal discs with molecular spacers. Coupling between the microscale resonator and nanocavity in this nanoparticle-on-resonator (NPoR) scheme, reveals extreme near-field enhancements resulting in boosted SERS intensities. We anticipate that such near-field enhancements open new horizons in single-molecule photonic circuits and molecular optomechanics.

We discuss a compact QED system of Germanium Vacancy(GeV) centres coupled to high quality factor silicon nitride nanobeam Photonic crystal(PhC) cavities. Devices with a quality factor of 24,000 around the zero-phonon line of the GeV center in diamond are demonstrated with an efficient fiber-to-waveguide coupling platform. We also present a method for fiber-waveguide coupling that allows seamless transition of photons from optical fibers into photonics devices and vice versa. Our method uses conical tapered optical fibers (with a tapering angle of ∼ 4° ) that are coupled over ∼ 11μm to a silicon nitride (Si₃N₄) waveguide taper (with a tapering angle of ∼ 1° ) achieving upto ∼ 96% coupling efficiency.

We introduced tunable Fabry-Pérot resonator using metal-insulator-metal multilayer, in which the insulator is hydrogel foam of chitosan [1]. The chitosan, one of polysaccharide, is responsive to external humidity, so the thickness and refractive index of chitosan change in response to relative humidity (RH); this trait can be utilized to tune resonance wavelegths of the resonator. This tunable color filter can function as humidity sensor when incorporated with photovoltaic (PV) cell. The PV cell transmit input optical spectrum to output current, which enables to determine the relationship between RH h and Response S defined the change in current before and after injection of humidity: S = -0.00002*h^2+0.0046*h-0.0238. Therefore, the response may correctly indicate RH of ambient in real-time. The proposed sensor would be simple to fabricate and potentially have zero-power consumption due to combination with PV cell, which makes the sensor useful for monitoring RH in enclosed spaces, workplaces and storage areas.

This work studies a fibre laser platform for generation of controllable localised wave structures. It was found out that a figure-8 laser with two independently pumped active media allows precisely controllable generation of solitary-wave bound states of up to the 6th order. Nonlinear shortening of the temporal pulse separation was discovered when 3 or more bound pulses are generated. Shown are the peculiarities of transitions among pre-determined dissipative multi-soliton complexes occurring both with and without Raman wave generation. Provided are distribution maps of peak power and energy of stable bound waves depending on pump powers of the active media.

The simultaneous conversion circular dichroism and wavefront shaping play a vital role in light-matter interactions. The conversion circular dichroism achieved either by intrinsic chirality of nano-antennas or by using multilayer structures which have fabrication complexities. We propose a unique single-layered all-dielectric metasurface for circular asymmetric transmission in the visible regime. We introduce the combination of achiral structures as the building block of metasurface for the simultaneous conversion circular dichroism and wavefront modulation by utilizing hydrogenated amorphous silicon (a-Si:H). The proposed material is a low-loss and a CMOS compatible solution for realizing efficient all-dielectric metasurfaces for the visible domain. The demonstrated methodology exhibits highly efficient transmittance under right circularly polarized (RCP) illumination while completely blocking the light for the opposite spin of the incident light. The multifunctionality of the proposed metasurface can provide a promising route for chiral imaging, CD spectroscopy and spin-selective optical systems.

The Z-scan measurement technique is a scanning method used to know the non-linear optical behavior due third order process in different materials, some of these behaviors are: as saturable absorption, reversible and non-reversible absorbers, absorption of more than one photon, among others. This technique is based on the displacement of the sample in the direction of propagation (Z) of a laser light beam. In this work the study of the nonlinear properties of three samples was carried out through this technique using a continuous wave laser, with Gaussian profile, and emitting at λ = 1550 nm, the samples used were: ethanol, acetone, and distilled water. Nonlinear absorption and nonlinear refraction were observed for the three samples.

Active tunability of optical leaky wave antenna is highly desired to enable greater control on light-matter interaction, sensing, and communication. Phase-changing materials can be integrated in optical antennas to enable such tunability. Among the phase-changing materials, vanadium dioxide (VO₂) is the most useful as it shows the semiconductor to metal transition (68°C) very close to the room temperature. The phase transition in VO₂ can be commonly induced by optical pulses or electrical joule heating. VO₂ exhibits significant temperature-dependent electrical and optical coefficients even outside of the transition temperature making it suitable for both - fine and coarse tuning of the properties of optical devices depending on the temperature bias. In this work, we study optical leaky wave antenna consisting of a silicon nitride waveguide with periodic VO2 nanowire perturbations. We present the numerical analysis of different arrangements of the periodic perturbations. The antenna operates by the coupling between the evanescent mode of the waveguide and the nanowires. We show that, by selective joule heating of individual nanowires we can tune the optical property of corrugations and enable wider tuning range and higher degree of control on the radiated beam. We also include a comparative study to show tunability and performance of the antenna with different phase-changing materials like vanadium pentoxide (V₂O₅) and germanium-antimony-tellurium (GST). We show that, around the phase transition temperature of VO₂, the directive gain of the antenna can be modulated by up to 25 dB and the radiation peak position can be tuned by up to 2.3°.

Metal tip based near-field scanning microcopy (NSOM) has been proved to be a convenient platform for surface plasmonic nano-cavity (SPNC) contributing the extremely high E-field enhancement to sub-nanometer spatial resolved imaging. Although the linear polarized laser illuminated from side with large angle was commonly employed, the unexpected E-field component (parallel to substrate but vertical to tip) was hard to avoid. Alternatively, we focused the vortex laser beam with radial polarization directly to the tip apex from wafer side, and hence we could generate a much purified longitudinal E-field. The consistency of polarization direction inducing gap-mode charge oscillation was otherwise close to 100%. However, the overall “hot-spot” enhancement depended on the balance between mode volume and transmittance. We thus theoretically detailed this issue, leading to the corresponding optimization methodology for the final enhancement. Furthermore, we extended this approach into more general tip-free gap-mode, such as gold nanoparticles on a gold film. Via using SPNC, the Second Harmonic Generation (SHG) from asymmetry boundary could be easily amplified by orders. However, the surface plasmons (SPs) involved nonlinearity were limited by not only symmetry rule, but the eigen-mode of SPs as well. Although the SP based SHG model of single nanoparticle had been well established, the gap-mode induced SP-SHG was rarely reported, as the phase matching and mode matching were challenging to satisfy simultaneously. Taking advantage of vortex beam, we successfully detected the distinguishable SHG signal, and more, realized the mapping imaging.