This PDF file contains the front matter associated with SPIE Proceedings Volume 11796, including the Title Page, Copyright information, and Table of Contents

Twisted bilayer graphene has recently been extensively investigated due to its unusual physical properties. In this talk, we will discuss its infrared optical properties and its potential in mid-infrared light detection. We first show that the folding of the Brillouin zone leads to enhanced density of states and strong mid-infrared light absorption, which are tunable by the twist angle. Furthermore, we reveal the significance of the formation of superlattice bandgap. Strong mid-infrared photoresponse is observed when the Fermi-level is within the superlattice bandgap. On the contrary, when the superlattice bandgap is vanished, the photoresponse is minimized. Our demonstration provides an alternative pathway towards the realization of high performance mid-infrared photodetectors.

Plasmons in graphene are known to be tunable and to exhibit extreme field confinement, making them useful for optoelectronic devices, and for exploring extreme light matter interactions. Thus far, these effects have been demonstrated at Thz to mid-IR frequencies, with the upper frequency limit set by limits of electron beam lithography, which can make graphene nanostructures as small as 15nm. In this talk, I will show that bottom-up block co-polymer lithography methods can create nanostructures with characteristic lengthscales as small as 12nm, and that in this regime the non-local interactions in graphene become strong, creating a significant blue shift of the plasmonic resonances. This allows for the creation of plasmonic cavities with resonances at wavelengths as short as 2.2um. The confinement factors of these cavities reach 135, which is exceedingly large, but less than what has been predicted by theory.

We present the design and the numerical modeling of electrically-tunable plasmonic metasurface absorber based on the Babinet’s principle in the mid-infrared spectrum. The plasmonic metasurface consist of an array of gold nanoantennas on a dielectric layer followed by gold substrate in a metal-insulator-metal (MIM) configuration. A graphene layer placed on top of the array enables electrical tuning of the antenna optical response. Finite-difference time-domain (FDTD) -based simulations were carried out using a commercially implemented FDTD Solutions to obtain the optical response of the metasurface. Based on the Babinet’s principle, we design and numerically modeled the complementary metasurface. We found that, even with the graphene layer, the complementary metasurfaces comply with the Babinet’s principle. These metasurfaces can found application as electrically-tunable sources in the mid-infrared range.

In this talk, I will introduce MoO3 as an anisotropic photonic and polaritonic material. MoO3 is a layered material that exhibits both in and out-of-the-plane anisotropic polaritonic response at mid-IR wavelengths. We designed and experimentally demonstrated an anisotropic polaritonic absorber and showed that one can couple to all phonon modes and address them individually either using structural tunability or polarization control of incident infrared radiation. I will also discuss our experimental investigations of the birefringent optical properties of MoO3 in visible frequencies. By constructing MoO3 based Fabry-Perot resonator, we observed strong polarization-dependent tunability of the Fabry-Perot resonance due to different refractive index of MoO3 for different crystal directions.

The combination of quantum materials and metasurfaces promises intrinsically new functionalities, driven by the wide range of novel phenomena inherent to quantum materials and the ability to control them with metamaterials. Two-dimensional (2D) quantum materials, such as graphene and transition metal dichalcogenides, have attracted much attention in this respect due to their ability to replicate nearly all of the properties of bulk quantum materials at the nanoscale and the relative ease in combining them with one another as well as incorporating them into new device architectures. Here, I will describe our recent studies combining 2D quantum materials and metasurfaces to achieve new and enhanced functionalities, including tunable THz transmission and Faraday rotation in graphene microribbon-based metasurfaces and control over exciton emission/dynamics in WSe2 monolayer/metasurface structures.

This talk will discuss recent work on optical phenomena and photonic devices made from 2D chalcogenides (e.g., halide perovskites and carbon nanotubes) as well as 1D excitonic semiconductors. I will present how 1D nanostructuring of excitonic 2D semiconductors into nanophotonic dielectric gratings can enable exploration of new regimes of light-matter confinement including formation of hybrid exciton-plasmon-polariton states. This discussion will be extended to superlattices which are scalable over large areas. Further we will show that the light-matter hybridization persists in emission of direct gap 2D semiconductors such as hybrid halide pervoskites. Finally I will present our recent work on nanotubes and show dynamic tunability of their optical properties. I will conclude by giving a broad perspective on future prospects of 2D materials from fundamental science to applications.

Room temperature stable excitons near the K-point in few layer transition metal dichalcogenides (TMDs) such as WS2 dominate their optical response and offer a unique route for engineering light and matter interactions. To this end, we will discuss the observation of self-resonant exciton polaritons in 3L WS photonic crystals supporting a Fano type optical resonance. While the strong excitonic absorption allows for the experimental observation of exciton-polaritons, the valley coherent excitonic photoluminescence in few layer WS2 provides a unique mechanism for the investigation of valley coherent propagation of exciton polaritons.

Two-dimensional van der Waals (vdW) materials have emerged as a very attractive class of optoelectronic material due to their extraordinarily strong interaction with light. In this talk we will present our recent work on strong light-matter coupling and control of the excitons in 2D transition metal dichalcogenides. Specifically, we will discuss nonlinear optical response of the strongly coupled states, control of chiral light-matter interaction in these materials using metamaterials, and the use of strain and artifical gauge fields to control transport and valley properties of the excitons.

Single or few molecular layers of transition metal dichalcogenides (2D TMDs) can exhibit exceptional properties, including strong optical nonlinearities, large exciton binding energies and spin-valley polarization. Due to their flat nature, they are natural candidates for integration with photonic metasurfaces. In such hybrid systems, the metasurface can act to enhance and tailor the interaction of light with the 2D-TMDs. Vice versa, the 2D-TMDs can add additional functionality, such as light emission, nonlinear response, and tunability to the metasurface system. In this talk, both extended 2D-TMDs integrated with plasmonic or dielectric metasurfaces as well as laterally nanostructured 2D-TMDs will be discussed.

We present a novel technique for formation of sub-micron-sized lateral heterostructures in 2D semiconductors without fabrication complications of conventional approaches. We demonstrate the experimental formation of these heterostructures with unprecedented flexibility in shaping and sizing in different transition-metal dichalcogenides (TMDs). Some unique features include precise wafer-scale positioning with in-plane confinements well below 50 nm in mono-layer films. We discuss the possible challenges and opportunities in forming optoelectronic devices in this platform and comment on the extension of this approach to other classes of materials. This material platform can enable the long-sought quantum devices in atomically thin materials.

III-Nitride based photonic crystals or metamaterials can operate in the visible and ultraviolet frequencies and are important for many nanophotonics applications. A key challenge in efficient operation of such III-nitride based optical nanostructures has been in creating a low refractive index interface cladding region between the high refractive index substrate GaN and the active layer due to a lack of compatible natural low index materials unlike those in Si and III-V systems. Here we will discuss achieving such optical substrate isolation in III-nitride nanophotonic devices using electrochemical and photo-electrochemical etching techniques [Opt. Mat. Exp. 2018, 8, 3543]. We will describe the fabrication of a GaN nanowire array utilizing this method of optical isolation and present the optical response to demonstrate the effectiveness of this approach. Sandia National Laboratories is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

This Conference Presentation, “Directed and focused light emission from GaN quantum well metasurfaces,” was recorded at SPIE Optics + Photonics held in San Diego, California, United States.

Building heat management is responsible for approximately 15% of the global energy consumption and greenhouse gas emission. This energy consumption can be reduced if buildings can directly utilize the renewable thermal source/sink from the sun (solar heating) and the deep space (radiative cooling). This concept of "net-zero-energy" buildings requires a significant amount of research efforts in photonics and materials science. In this talk, I will introduce our recent work on the dynamic selective absorber that can control the absorption/emission spectral property from UV to mid-IR and electrochemically switch between solar heating and radiative cooling. For solar heating, the device has the ideal property of a selective solar absorber that absorbs strongly in the solar spectrum and emits poorly in mid-IR. For radiative cooling, the solar absorptivity decreases, and the mid-IR emissivity increases. The working principle is based on electrochemically reversible deposition of plasmonic nanoparticles that have broadband resonance in solar spectrum but act as a continuous metal film in mid-IR based on effective medium theory. For basic science, our work interrogates the fundamental interface chemistry to achieve the nanoparticle deposition and performs numerical modeling to guide the structure design. For application, if used as a smart building envelope, this device can switch and adapt to different weather, solar radiation, and occupant preference, thereby maximizing the utilization of renewable heat/cold sources.

In this talk I will discuss our group’s work on the design, growth, fabrication and characterization of a new class of all-epitaxial plasmonic optoelectronic devices with enhanced performance when compared to state-of-the-art infrared optoelectronics. Specifically, we demonstrate that highly doped semiconductors, serving as ‘designer’ plasmonic materials, can be monolithically integrated with a range of infrared optoelectronic device architectures to provide strong field confinement, and enhanced emission, detection, and potentially modulation capabilities in the mid-infrared. We will present results from long-wave infrared detectors with thickness of only 350 nm, capable of over 50% external quantum efficiency and state-of-the-art detectivity, as well as dual color detectors, spectrally-selective detectors, and enhanced efficiency emitters leveraging our designer plasmonic materials with a range of novel device architectures.

Strainoptronics is an emerging concept that allows to manipulate and hence engineer a plurality of materials properties such as the bandgap, mobility, and Schottky barrier height for example. 2D materials are especially utilizable for strainoptronics given their low dimensionality leaning to a strong (2-4%) ‘strainability’. Here I share our latest device demonstrations including (a) a efficient TMDC photodetector at 1550nm wavelength on Silicon PICs (Nature Photonics), (b) engineering the Schottky barrier height and reducing the bandgap by 200meV (arXiv: 2012.07715), and (c) showing scaling laws of scaling-length-theory based slot detectors with a potential for high gain-bandwidth-product PIC-integrated photodectetors (Opt. Mat. Exp. 2020).

We describe active photonic platforms based on structured nano-arrays with periodicities in optical dimensions. Nanocup arrays coated with continuous non-conformal gold films were fabricated with replica molding and simulated with scattering matrix simulations. These exhibit extraordinary optical transmission (EOT) due to the optically thin gold film at the nanocup bottom. The optically enhanced field in nanocups enhanced the spontaneous emission of embedded quantum dots, with Purcell factor enhancements by >80 and measured photoluminescence lifetimes decreased by a factor of ~5 for a quantum dots ensemble. Soluble coatings on these nanocups showed slowed release rates, useful for biomedical applications. Nano-arrays control active light-emission, and surface charging and have promise for diverse nanoplasmonic applications.

In this talk I will overview our ongoing theoretical and experimental work on light manipulation with bulk transition metal dichalcogenides (TMDCs). Specifically, I will show that owing to their high refractive index and strong anisotropy, structures made of bulk TMDC offer >30% stronger light confinement as compared to conventional semiconductor counterparts, paving the way to higher integration density and energy efficiency of optical devices. Several different types of classical and quantum structures made of TMDC materials, including waveguides, modulators and nanoscale cavities for quantum light emissions are discussed.

Periodic arrays of nanostructures can support collective modes known as lattice resonances that produce strong and spectrally narrow responses. Thanks to these exceptional properties, periodic arrays are being exploited in a wide variety of applications, including ultrasensitive biosensing, nanoscale light emission, and color printing, to cite a few. In this communication, we will analyze how the arrangement of the particles within the unit cell of the array determines its optical response [1-3]. We will also discuss how the interplay between the response of the individual constituents and the collective interaction dictates the ultimate limits of the field enhancement provided by these systems [4,5]. [1] S. Baur, et al., ACS Nano 12, (2018). [2] A. Cuartero-González, et al., ACS Nano 14, (2020). [3] L. Zundel, et al., ACS Photonics 8, (2021). [4] L. Zundel, et al., J. Phys: Photonics 1, (2019) [5] A. Manjavacas, et al., ACS Nano 13, (2019).

Absorption, spontaneous emission and stimulated emission are the paramount light-matter interactions encountered in photonics. Here, we theoretically investigate those three pre-cited phenomena inside unbounded media with a vanishingly small refractive index (NZI materials). Our formalism describes the effect of the spatial dimensionality of the NZI medium as well as the class of NZI materials (epsilon-near zero, mu-near zero or epsilon and mu-near zero). For example, spontaneous emission might be inhibited in 3D homogeneous lossless NZI media but be greatly enhanced in an NZI material of reduced dimensionality.

Periodic wavelength-scale surface patterns have long been used in the context of lasing and spontaneous emission to enhance emission by light trapping (distributed Bragg resonances). Buried within these well-known devices, however, are theoretical mysteries that are still being unravelled. A periodic surface grating actually creates a continuum of resonant modes, so what determines which single mode (if any) lases? Technically, what determines the stability of a periodic lasing mode: is it only the finite size of a surface that allows single-mode lasing, or can it arise for arbitrarily large structures? More generally, if one continuously deforms an unpatterned surface to maximize light emission, how is the symmetry broken and what optimal structures arise? We address these questions by combining new computational techniques for modeling and large-scale optimization of incoherent emission and lasing with new analytical results arising from perturbation and stability theory.

In-situ observation of light-induced physico-chemical changes is a long sought experimental approach to gain mechanistic understanding of the underlying fundamental processes. Here, we present experimental results that demonstrate the possibility of using plasmonic nanocavity for inducing and observing physical and chemical changes. This is demonstrated by monitoring photons scattered by a plasmonic nanocavity, in which materials of interest (organic and inorganic systems) are embedded.

Plasmonic nanomaterials and quantum metamaterials have the unique ability to confine light in extremely sub-wavelength volumes and massively enhance electromagnetic fields. The talk will discuss the principles of room-temperature strong coupling quantum dynamics in structured environs and illuminate perspectives for nanophotonics and topological quantum metamaterials with quantum gain on the nanoscale. We will highlight recently demonstrated room-temperature strong coupling of single molecules in a plasmonic nano-cavity and near-field strong coupling of single quantum dots as well as strong coupling and exceptional points in active hyperbolic metamaterials. We will discuss the electron-beam control of plexitonic dynamics and further present a new protocol demonstrating how nanoplasmonic room-temperature strong coupling offers an innovative route towards single-molecule immunoassay sensing and dynamic quantum entanglement.

The high Q of microcavities, and the ultimate confinement of plasmonics may be advantageously combined in hybrid photonic-plasmonic resonators for ultrastrong light-matter interactions for SERS, polaritonic chemistry, and novel light sources. I will present the unique merits of hybrids on basis of plasmonic-nanoparticle-on-mirror systems in cavities as compared to simple metasurface etalons and constructs on basis of dielectric microdisk cavities and simple dipole antennas. I will discuss experimental evidence from linear mode spectroscopy, femtosecond SHG and two photon luminescence studies, and SERS, and will provide a viewpoint on potential uses for sideband-resolved molecular optomechanics.

Integrated photonics is a powerful platform for future quantum technology that encodes and processes information using single photons. In this talk I will describe an experimental realization of a quantum transistor, which mediates strong interactions between single photons using a single semiconductor spin qubits. These interactions are a key requirement for active quantum photonic devices. I will also present our recent work on hybrid integration of these devices with photonics, as well as applications in photonic quantum computing and topological photonics.

Epsilon-near-zero (ENZ) materials have been key players in recent photonic applications due to their versatility in growth, excellent compatibility, and ability to be dynamically modulated. From a foundation in the recently developed carrier kinetic models of nonlinearities in ENZ materials, we discuss our efforts to realize scalable and high-quality Al:ZnO (AZO) films via a unique atomic layer deposition (ALD) process, and the use of AZO in both switching and frequency shifting applications. Throughout, we highlight the advantages and challenges that exist and conclude with an outlook for ENZ materials in the area of nonlinear optics.

Methods currently used to determine nonlinear optical constants like n2 or chi3 rely on open and closed z-scan techniques. The study of optics at the nanoscale in the femtosecond regime requires new tools and approaches to extract linear and nonlinear dispersions exhibited by matter. We present a practical approach that amounts to numerical ellipsometry that utilizes experimental harmonic generation conversion efficiencies to retrieve complex, nonlinear dispersion curves. We provide examples of retrieved linear and nonlinear dispersions for a variety of materials, and show that for Silicon the numerical retrieval method yields chi3~10^(-16) (m/V)^2 and chi33w~10^(-17) (m/V)^2 , and visible and near IR ranges. Similarly, we predict chi3~10^(-17) (m/V)^2 and chi33w~10^(-19) (m/V)^2 for ITO as it exhibits linear and nonlinear anisotropic responses due to nonlocal effects.

The future of photonic devices involves harnessing non-linear effects, for applications such as frequency upconversion and down-conversion, optical switching, and emission control. To effectively do this, the optical properties of designed material systems are needed. Metamaterials can be fabricated in a layered form to operate in many wavelength bands, and they exhibit strong non-linear effects. To make the layered metamaterial, alternating layers of metal and dielectric were used. Samples were fabricated using physical vapor deposition for the material system ITO-SiO₂, with varying layer thicknesses for each sample. First, the linear properties of the samples were measured using variable angle spectral ellipsometry, and then the non-linear properties were measured using the Z-scan technique. The linear results show a good agreement with effective medium theory, which signifies that the metamaterials are suited for computer-aided design. Also, the non-linear results show strong non-linear properties, of n₂ = 1 ∗ 10¹⁴ cm²/W, and β = 2 ∗ 10¹⁰ cm/W, which is larger than many natural materials. This demonstrates the potential for use in non-linear applications.

Since the emergence of nanoscale photonic systems to tailor light at-will, electro-optic transducers have become critical components to link the optical domain further with the electronic domain. Many electro-optic transducers have been reported for integrated photonic circuits that are ideally suited for fiber-based applications. Instead, free-space electro-optic transducers could target entirely different applications that require a combined in-plane and time-domain control of freely propagating light at high speeds. Here, we demonstrate nano-engineered free-space electro-optic transducers that combine low-loss dielectric Mie resonators arranged into a meta-array and high-performance electro-optic molecules. We discuss how various design parameters influence the tuning of optical resonances which we show to reach up to 20 nm at a center wavelength of 1550 nm.

Here we present high quality factor (high-Q) metasurfaces as a new platform for continuous, electro-optical reconfigurability. Using full-field simulations, we show how applying a voltage across individual nanoantenna shifts the spectral position of the high-Q resonance, modifying the antenna phase and amplitude, and achieving a full 2 pi phase variation with reflectance above 93%. We next computationally design a modulatable beam steerer; without bias light is directly reflected from the metasurface, whereas with applied biases of +9.2, 0, and -9.2 V across three constituent antennas the light is diffracted to 30 deg with 65% efficiency. Biases of 13, 2, -2, and -13 V across 4 constituent antennas diffract to 22 deg. Our presentation will discuss not only the design but also fabrication and characterization en route to a versatile metasurface platform that can reconfigurably achieve a variety of transfer functions.

Nanostructures made of semiconductors or metals are nowadays routinely integrated in photonic devices. At this scale light-matter interaction displays interesting new phenomena. We report a collection of experimental results of nonlinear harmonic generation in different nanolayers: semiconductors, conductive oxides and metals. The comparison of these experimental results with numerical predictions of our theoretical model identifies, distinguishes and explains the different nonlinear contributions to the harmonics generated by these materials at nanoscale. Our model accounts for surface, magnetic and bulk nonlinearities arising from free and bound charges, preserving linear and nonlinear dispersion, nonlocal effects due to pressure and viscosity.

Unique optical properties of optical nanostructures open unlimited opportunities for sculpting light. We discuss recent developments in passive and active nanophotonic structures that allow dramatically altering such properties of light as amplitude, phase, polarization, frequency and angular momentum. First, we consider linear and nonlinear optical metasurfaces, nano-patterned layers with subwavelength thickness that enable versatile control of the topology of light as well as novel regimes of frequency conversion. Next, we discuss our recent studies of orbital angular momentum microlasers and laser arrays based on the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking. These studies may provide a route for the development of the next generation of optoelectronic devices for classical and quantum communication systems.

We demonstrate an embedded one-dimensional (1D) topological photonic structure based on a III-V photonic crystal (PhC) lattice on silicon. Localized emission is detected from the topological state which forms at the interface between two lattices with different topological invariants, whereby this single mode is centered in the photonic bandgap. The 1D beam structure significantly reduces the area compared to a 2D structure, which together with our embedded fabrication platform is an important metric for future dense integration. The emission from this topological mode shows evidence of lasing in the telecom O-band with the threshold of around ~14 μW at room temperature. Compared to a similar trivial PhC structure, the topological design is inherently single mode. We evaluate the robustness of the topological resonant mode by introducing a defect right at the interface, which does not affect the existence of the topological state.

Future technologies underpinning high-performance optical communications, ultrafast computations and compact biosensing will rely on densely packed reconfigurable optical circuitry based on nanophotonics. For many years, plasmonics was considered as the only available platform for subwavelength optics, but the recently emerged field of Mie resonant metaphotonics provides more practical alternatives for nanoscale optics by employing resonances in high-index dielectric nanoparticles and their structures such as metasurfaces. In this talk, I hope to discuss both recent advances and future emerging directions in the physics of dielectric Mie-resonant nanostructures with high quality factors (Q factors) for efficient spatial and temporal control of light by employing multipolar Mie resonances and bound states in the continuum, with applications of these concepts to nonlinear optics, active photonics, and topological lasers.

Coupled loss and gain resonators can exhibit parity-time (PT) symmetry and exceptional points, and find rich applications in sensing, lasing and quantum optics. This talk presents an intuitive and powerful quasinormal mode theory for coupled loss and gain resonators, including a quantitatively accurate coupled mode theory using quasinormal modes. As an application of the theory, we demonstrate extremely rich spectral lineshapes and Purcell factors for coupled loss-gain microdisk cavities. We then point out a fundamental flaw in currently adopted theories of spontaneous emission in absorptive and amplifying media, and present the corrected Fermi's golden rule, one that requires a fully quantum mechanical description.

Reciever protectors (RP) shield sensitive electronics from high-power electromagnetic signals that might damage them. Typical RP schemes range from simple fusing and PIN diodes to superconducting circuits and plasma cells -- each having a variety of drawbacks ranging from unacceptable system downtime and self-destruction to significant insertion losses and power consumption. We introduce a class of non-Hermitian photonic receiver protectors that are self-protected from overheating effects induced via high-level incident electromagnetic radiation, due to a self-regulating impedance mismatching mechanism that turns them into near-perfect reflectors. At low-power incident signals, these receiver protectors demonstrate high transmittance via a nonlinear defect mode. In this limit, they also demonstrate a high tolerance to fabrication imperfections due to topological protection, imposed via a charge-conjugation symmetry.

This paper will report on some features of a platform for the realization of an anti parity-time (anti-PT) symmetric system in a pair of time-delay coupled semiconductor lasers, with special emphasis on the delay induced dynamics in the system. The system is modeled by a modified Lang-Kobayashi rate equations model, augmented to include delayed coupling. The role of a phase accumulation factor that arises from the delayed coupling is elucidated. Finally, the novel exceptional point(s) behavior that is characteristic of the time-delay is investigated via numerics as well as analytically via the Lambert W function.

A feasible restricted Hilbert Transform (HT) is presented to solve the challenging practical realization of non-Hermitian systems, restricting the complex susceptibility within practical limits. Beyond closed-conservative systems, the physics of non-Hermitian systems has become the playground to uncover unusual phenomena. Whilst Kramers Kronig relations break the temporal symmetry leading to causality, we proposed an analogous generalized Hilbert Transform (HT) to engineer complex media holding a non-isotropic response, thus breaking the spatial symmetry. Applications of such HT range from tailoring the field flows in arbitrary dimensions with particular application on VCSELS and edge-emitting lasers to cloaking arbitrary objects.

A versatile approach for engineering the coupling dynamics in active cavities is proposed and experimentally demonstrated. 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.

The concept of parity-time (PT) symmetry has recently expanded the toolbox to achieve active tunability in metasurfaces by modulating the imaginary part of the refractive index. In this work, we propose a hybridized static-active platform to dynamically tune the intensity and angular response of light by varying the non- Hermiticity factor in an all-dielectric metasurface. We numerically demonstrate tunable asymmetric transmission with respect to gain or loss side incidence in a vertically stacked Mie-resonant GaInP phased-array metasurface. It should be noted that the proposed system is reciprocal despite asymmetric transmission as the materials considered are in a linear regime. The primary building block consists of four PT-symmetric nanopillars of varying radii to achieve sufficient phase sampling. The overall design parameters are optimized for operation at a wavelength of 655 nm (typical PL emission peak of GaInP). For loss side normal incidence, the transmission is predominantly in the 0^th diffraction order (η^l₀~ 0:80, η^l₁~ 0:18), while for gain side normal incidence, an amplified transmission is in the 1^st order (η^g ₀~ 0:02, η^g ₁~0:78). The observed asymmetric transmission is due to the near-field coupling between different Mie multipoles, broken in-plane mirror symmetry (meta-atoms with increasing radii along the x-axis), and the broken PT-phase along the propagation direction. An asymmetry factor, ~0:9, is observed at λ = 655 nm. The symmetry in transmission can be restored by reducing the gain-loss contrast. We believe an optimal arrangement of gain-loss resonators combined with tunable pumping (either optically or electrically) could pave the way towards practical reconfigurable metasurfaces.

We investigate the exceptional points in a two-layer cylindrical waveguide structure consisting of absorbing and nonabsorbing dielectrics. We show that by tuning the parameters of the structure the complex effective indices of two waveguide modes can coalesce so that an exceptional point is formed. We show that the sensitivity of the effective index of the waveguide mode is enhanced at the exceptional point. We also investigate using phase-change materials in multilayer structures to switch between singular points. We show that in multilayer structures consisting of phasechange, lossless dielectric, lossy, and gain materials, absorbing or spectral singularities can be switched to exceptional points, and self-dual spectral singularities can be switched to unidirectional spectral singularities by switching the phasechange material from its crystalline to its amorphous phase. Our results could be important for developing new compact reconfigurable singularity-enhanced optical devices.

Recently, time has emerged as a new degree of freedom for metamaterials, as variations of the electromagnetic parameters in time as well as in space allow for new pathways in wave control. In these time-dependent systems, energy is not necessarily conserved, and the linear bias imposed by travelling wave modulations permits non-reciprocal effects in the absence of external magnetic fields. I will present a theory of homogenisation of space-time metamaterials, which provides analytical expressions for the effective permittivity, permeability and magnetoelectric coupling in the long wavelength limit. From the derived parameters I will show how it is possible to bring nonreciprocity down to zero frequency if both the permittivity and permeability are modulated, and how the synthetic motion present in these systems enables a Fresnel drag effect of light without moving matter. Thus, giant magnetoelectric effects emerge without external magnetic biases or relativistically moving matter.

Recent years have witnessed significant interest in topological insulators (TIs), a new form of mater with low scattering states along their edges. This property can be useful for the design of passive or active devices, like defect-tolerant waveguides or lasers with robust extended lasing modes. In this talk we will discuss another interesting application of TIs, namely synchronization of oscillators. We will show that connecting oscillators along the edges of TIs allows their synchronization via the TI edge states with low sensitivity over the oscillator locations and perturbations of their parameters. We will present results for the nonlinear dynamics of such systems and outline potential applications in phased array antennas.

This Conference Presentation, “Self-induced vortex and anti-vortex singularities in laser arrays,” was recorded at SPIE Optics + Photonics 2021 held in San Diego, California, United States.

We consider the topological aspects of wave propagation in 1D photonic crystals. It was shown by Zak that in 1D structures, bands could be characterized by means of a geometric phase, provided the structure possesses an inversion symmetry, that is the potential V is symmetric with respect to some point. This phase is defined as an integral over the Brillouin zone. We propose another view on the Zak phase, based on a dynamical system approach, that allows to identify the topological properties with the presence of poles of a meromorphic function. This allows to extend the notion to lossy systems. Numerical examples are given in the case of 1D structure whose basic period comprises two slabs filled with a homogeneous material.

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 the so-called photonic higher-order topological insulators (PHOTIs) enabling light localization at their corners. I will discuss several examples of the PHOTIs based on coupled microwave cavities (emulating quadrupolar insulators) and new PHOTIs based on topological crystalline insulators emulating spin-orbit coupling. Strategies for developing nanoscale PHOTIs will be discussed, including metagate-controlled 2D materials. Finally, a novel regime of quantum landscaping of single-layer graphene, where periodic patterns of chemical potential simultaneously modify electronic and photonic propagation bands, will be introduced.

This Conference Presentation, “Compact localized states and dynamics in complex photonic lattices with multiple flatbands,” was recorded for Optics + Photonics 2021, held in San Diego, California, United States.

Topologically tailored photonic crystals offer robust transport of optical states in quantum and classical systems. However, quantifying the robustness of edge states in topologically protected PhCs has remained elusive. In our recent work, we report a rigorous quantitative evaluation of topological photonic edge eigenstates, emulating the quantum valley Hall effect (VPC), and analyze their transport properties in the telecom wavelength range using a phase-resolved near-field optical microscope. Our results demonstrate that the backscattering energy ratio for the VPC is two orders of magnitude smaller compared to that in a conventional W1 waveguide. Such an evaluation opens a pathway for creating quantum photonic networks that can achieve secure and robust communications.

Bringing topological physics from condensed matter to the optical domain offers unprecedented prospects in the control of light. Recently, the photonic analogue of the quantum spin Hall effect (QSHE) was proposed in 2D photonic crystal (PhC) structures featuring an interface between two topological distinct domains. Photonic spin-orbit coupling, mediated by the specific lattice symmetries, results in the emergence of helical edge states, guided along the interface in a protected manner. We fabricate and study topological PhC cavities emulating the QSHE that are coupled to the radiation continuum and perform imaging and Fourier spectroscopy in the far field to characterize their properties. We examine the robustness of cavity spectra and intrinsic loss against varying cavity size and shape, and demonstrate pseudo-spin conserved coupling between topological waveguides and cavities. The reliance on only passive media render such components promising building blocks for on-chip devices.

Photonic crystal slab (PCS) waveguides can be engineered to control the propagation of light, finding a variety of applications in optical sensing, nonlinear optics and quantum optics. However, traditional PCS waveguides suffer from disorder-induced backscattering which is especially severe in the slow-light regime. Topological PCS waveguides can support propagating edge-state modes which are possibly more robust against some defects. Here we apply inverse design techniques to modify a state-of-the-art topological PCS waveguide, to obtain a significant (more than 100%) improvement to the operational bandwidth of a lossless waveguide mode. We then optimize the new design's group velocity curve, obtaining two new designs, one with a group index of 28 over a bandwidth ▵ω/ω=1:5% and in the other a maximum group index greater than 200 away from the mode edge. We use an efficient, semi-analytic, computation method, the guided mode expansion method, to calculate photonic band structures and automatic differentiation to calculate objective function gradients. Combining this with a physically intuitive shape parameterization, the method, while initially constraining the optimization to solutions resembling the initial design, is efficient and flexible. This method can be applied to quickly optimize PCS devices towards a large variety of target figures of merit.

Topological photonics/acoustics utilizes classical waves to emulate topologically nontrivial phases originally developed in condensed matter systems such as topological insulators. While the band topology concepts are originally defined in Hermitian context, the classical-wave systems are intrinsically non-Hermitian, due to the inevitable loss and/or deliberately added gain. Here we will introduce some of our recent works in developing acoustic topological states that have no counterparts in condensed matter systems. The first is about non-Hermiticity-driven topological phase transition. This involves the demonstration of topological edge states in a 1D acoustic lattice and topological corner states in a 2D acoustic lattice. The second is about acoustic non-Hermitian skin effect from twisted winding topology. The twisted winding topology consists of two oppositely oriented loops with a contact point in between. We show that this topology dramatically modifies the non-Hermitian skin effect by causing bulk states collapse towards two directions. The contact point corresponds to an extended Bloch-wave-like bulk states. The third is a Floquet higher-order topological insulator realized in a 3D acoustic structure, whose third dimension serves as an effective time-dependent drive. All the above show novel topological physics on the platform of acoustic waves.

Stimulated Brillouin Scattering (SBS) – a strong nonlinear optical effect – has recently emerged as a powerful signal processing technology with applications in defence, medicine, sensing and communications. Brillouin scattering couples efficiently between light (photons) and sound waves (acoustic phonons). This coupling only occurs over a narrow frequency range which makes Brillouin physics ideal for sensing technologies, and is emerging as a critical enhancement for microwave processing applications where it provides the high-resolution, bandwidth flexibility, and reconfigurability which are major bottlenecks of state-of-the-art systems. SBS is only now starting to be harnessed in centimetre-scale integrated devices with impressive demonstrations based on silicon and chalcogenide integration, enabling unprecedented efficiency and promising significant reductions in SWaP. This talk reviews recent progress and achievements as well as challenges and opportunities.

We study the emergence of nonreciprocal and topologically nontrivial phonon transport in nano-optomechanical networks. We develop on-chip nanophotonic systems in which multiple mechanical modes are strongly coupled through radiation pressure. Through temporal modulation and retardation, suitable laser control fields can break time-reversal symmetry and introduce controlled gain and loss at will on any of the network link and nodes. We reveal the emergence of nanomechanical circulation, helical quantum Hall states, and chiral thermal transport. Exploiting optomechanical gain, we study the combination of broken time-reversal symmetry and non-Hermiticity. This leads to rich phenomenology including magnetic-field tuning of exceptional points and unidirectional phononic amplification. It promises to serve as building blocks for new bosonic topological phases in the domain of nanomechanics, which is rich in applications in sensing and signal processing.

The ability to describe optical cavity physics in terms of normalized modes and cavity figures of merit has played a key role in laser optics and cavity quantum electrodynamics. In mechanics, however, cavity mode theories are less well developed. We will present some recent developments in the accurate modelling of mechanical open cavities. Using a quasinormal mode theory for mechanics, we accurately describe dissipative cavity modes while preserving their phase properties, providing a robust tool for describing coupled optomechanical cavities exhibiting complex elastic Fano resonances and exceptionally large enhancements of the mechanical quality factors.

Diamond optomechanical devices combine excellent optical and mechanical properties, allowing coherent conversion of information between optical and mechanical domains. Furthermore, they host colour centres that can function as long-lived quantum memories and qubits. By creating precisely engineered diamond optical cavities that also support low loss mechanical resonances, we have succeeded in both reversibly storing information in diamond optomechanical devices, and in optomechanically controlling diamond spin qubits. This talk will review both the fabrication and experimental challenges that needed to be overcome to realize these goals and will discuss on-going efforts to create diamond optomechanical crystal devices.

By introducing geometrical-scaling-induced phase modulations, we demonstrate in this work that an assembly of circularly polarized and linearly polarized states can be simultaneously generated by a single metasurface made of L-shaped resonators with different geometrical features. Each resonator of the metasurface diffracts either a right-handed or left-handed circular polarized states, with an additional phase modulation determined by its geometry features. The interaction of the diffracted fields leads to the desired output beams, where the polarization state and the propagation direction can be accurately controlled. As an example of potential applications, we show that an image can be encoded with different polarization profiles at different diffraction orders and decoded with a polarization analyzer. This approach resolves a challenging problem in integrated optics and is inspiring for on-chip quantum information processing.

It is shown that the onset of signal oscillations in the parametric nonlinear process of three-photon down-conversion is analogous with a first-order phase transition. Such an oscillator exhibits phase tristability, such that by reaching above the oscillation threshold it can take three different states with uniform phase contrasts. An analytically solvable second-order oscillator model is derived and the stability of the trinary phase states is proven through a Lyapunov function. The phase tristability of a three-photon down-conversion oscillator intrinsically emulates a classical trinary digit (trit). Such a trinary digit can be utilized for applications in unconventional computing.

Dissipative interaction facilitates the global phase locking of a network of lasers with generally complex graph topologies. Recently, we showed that the equilibrium states of such laser networks are optimal solutions of governing cost functions that are of non-convex quadratic form. This realization allows for mapping a large class of non-convex optimization problems onto laser networks, which provides a promising route for optically solving such computationally-hard problems. Here, by numerical simulation of the underlying dynamical equations, we investigate the accuracy of the solutions obtained for well-known non-convex problems and discuss the role of parameter tuning for escaping the local minima.

Associative learning as a building block for machine learning network is a largely unexplored area. We present in this paper our results on the demonstration of an all optical associative learning element, realized on an integrated photonic platform using phase change materials combined with on-chip cascaded directional couplers. We implement the framework on our optical on-chip associative learning network, and experimentally demonstrate image classification on a publicly-accessible cat-dog dataset. The experimental implementation harnesses optical wavelength division-multiplexing, thus increasing the information channel capacity to process our machine learning task. Our unconventional approach to machine learning demonstrated experimentally on an optical platform could potentially open up new research possibilities in machine learning hardware architectures and algorithms.

We show that wavevector-space metasurface can be used to achieve non-trivial correlation between the frequency and the momentum of light. As applications we demonstrate squeezing of free space, generation of meron textures, and creation of the three dimensional light bullets.

The challenge for biosensors is to achieve high performance and multiple functionalities at low cost, which includes the source and readout instrumentation. Here, we describe a sensor modality utilizing guided mode resonances that can detect multiple markers for infection, that combines the sensor chip and spectrometer in a single chip and that can achieve a limit of detection as low as 1pg/ml. This performance is equivalent or better than laboratory-based techniques yet the sensor and instrumentation can be made entirely from low-cost components.

We demonstrated the fabrication of thin-film stacks comprising mid-infrared-transparent dielectric layers and active optical materials, enabling the creation of tunable mid-infrared filters. In particular, we designed and fabricated an induced-transmission filter (ITF)—a dielectric thin-film filter that uses an ultrathin metal layer to remove unwanted sidebands around a desired passband—where the metal layer is replaced by a prototype phase-transition material, vanadium dioxide (VO2). We designed filters with one or more tunable passbands, and experimentally demonstrated a filter that switches between a broadband transmission window in the mid infrared (8 – 12 µm) and a narrow passband centered around 8.8 µm.

Conventionally, phase-change materials (PCMs) employed in active metasurfaces feature high optical contrast between their dielectric amorphous and crystalline phases. Here, we employ the non-volatile PCM In3SbTe2 (IST) which changes from dielectric to metallic upon crystallization in the whole infrared spectral range. We demonstrate the direct optical writing, erasing, and modifying of metallic IR nanoantennas in an IST thin-film, as well as switching from electric to magnetic dipole modes. We realize a tunable absorber and show nanoscale screening and “soldering” of pre-patterned meta-atoms. Our concepts enable rapid prototyping of infrared plasmonic meta-optics and may empower improved designs of programmable nanophotonic devices.

Optical phase change materials (PCMs) are a unique class of materials which exhibit extraordinarily large optical property change (e.g. refractive index change > 1) when undergoing a solid-state phase transition, and they have witnessed increasing adoption in active integrated photonics and metasurface devices in recent years. Here we report integration of chalcogenide phase change materials in the Lincoln Laboratory 8-inch Si foundry process and the demonstration of electrothermally switched phase-change photonic devices building on a wafer-scale silicon-on-insulator heater platform.

We propose gold-vanadium dioxide microstructured emitters for which the difference in thermally radiated power between two predefined temperatures can be made positive, negative or zero via structural design. The emitter geometry is based on incorporating VO2 in a gold-dielectric-gold waveguide. Such a waveguide exhibits a temperature-dependent mode effective index owing to the phase-changing behavior of VO2. This in turn causes our emitters to exhibit a strongly temperature-dependent emissivity. We use our emitters to design a metasurface with a thermally-invertible spatial emission pattern. Such emitters could be useful for several intriguing applications such as remote temperature monitoring and thermoelectric power generation.

In this work, we demonstrate the modulation in optical response at visible wavelengths of a dielectric grating structure under a thermal stimulus. The grating structure is coated with a thin layer of vanadium dioxide (VO₂) which undergoes a phase transition from an insulator to a metal at a temperature of ~ 68°C. We report on the design, simulations, and characterization of the proposed structure. Measured optical response through experiments finds a good agreement with the predictions made by numerical simulations.

Phase change materials (PCMs) are materials in which phase transitions can be induced quickly and reversibly, resulting in pronounced changes in their physical properties. PCMs have a diverse technological potential ranging from neuromorphic devices and efficient high-frequency electronics and opto-electronics to (re)programmable optical meta-materials. In this presentation we review our recent results on self-consistent multi-physics description of PCM based photonics including meta-surfaces for mid-infrared and infrared spectral ranges and integrated optics elements.

We investigate photonic design strategies for thermal emission control based on multi-resonator systems. Metamaterial resonators incorporating phase-change materials provide a temperature-tunable response. We identify a layer design for which the radiated power can be designed to either increase or decrease across a phase transition, simply by varying resonator length. Systems supporting both bright and dark modes offer increased design flexibility. We illustrate the use of tunable dark-dark coupling to extinguish thermal emissivity peaks.

We introduce a cellular automata methodology for studying the photonics of light-induced phase transitions. A model governed by a sparse set of evolutionary rules successfully describes the complex, non-stationary, spatially inhomogeneous dynamics and nonlinear optical properties of a medium undergoing a light-induced structural transition.

Chalcogenide phase change materials have many fascinating characteristics, i.e. extraordinarily large optical and electrical changes and non-volatility, making them appealing for information storage and reprogrammable photonics. Designing programmable photonics devices requires an accurate model to describe the switching behavior. Here, we present a multi-physics cellular automata-based framework which combines laser-induced heating, Gillespie’s Cellular Automata approach, effective medium theory and Fresnel’s Laws to model the microstructural evolution and concomitant optical response of phase change photonics devices. From the framework, we can simulate the change in optical constants during the phase switching process as well as the transient change in crystallite distribution, reflection, and transmission. The accuracy of the multi-physics model is also verified by nanosecond-pulsed laser switching experiments and transmission electron microscopy.

Active control of thermal emission can be realized by modulating either the temperature or the thermal emissivity of an object. This talk will first introduce a new spectroscopic technique—Planck spectroscopy—that measures the spectral emissivity of an object by changing its temperature. Planck spectroscopy uses only a temperature-controlled stage and a detector, without any wavelength-selective components such as prisms, gratings, or interferometers. Then, this talk will describe our efforts to achieve ultrafast control of thermal emission via emissivity modulation. By using free-career dynamics in semiconductors, we generated thermal pulses on nanosecond and picosecond scales.

Transient photonics entitles the controlled use of optical devices that can vanish on demand. Here, we demonstrate a platform for transient photonics based on Mg and MgO, materials that dissolve in water at ambient environment. We show vivid color pixels covering the entire sRGB, where the hues disappear in a few minutes upon system's exposure to water, important for applications ranging from encryption to eco-friendly displays.

Active metasurfaces designed to operate at optical frequencies are a new class of flat optical elements that can dynamically control the wavefront of the reflected or transmitted light at a subwavelength scale. Here, we estimate the feasibility of using gate-tunable conducting oxide metasurfaces as electrically steerable apertures for free space optical communications. Our optical link budget analysis shows that for pulse energies of 1 mJ, free space optical communication at distances of 100000 km is possible. We further elaborate our analysis by adopting a system design approach and refining our optical link budget analysis.

J-aggregates are supramolecular structures with great potential as building blocks made of organic materials for subwavelength confinement. Their extraordinary properties are related to the delocalisation of excitons between the monomers. It is possible to modify the arrangements of monomers by hydrodynamic forces obtaining a strong circular dichroism signal. In this work, we study how to tune this induced circular dichroism response as a function of the stirring velocity and the ionic strength of the dispersion media for a large variety of J-aggregates. The final aim of this work is to reflect the potential use of this chiral J-aggregates as building blocks for fluorescent tunable chiral-nanoprobes.

Resonant propagation of light is important for building novel light source and chip-scale optical interconnects. Here, we introduced an optoplasmonic amplifier which is operating in the visible range and generating Raman signal internally with injection seeding. We introduced the microspheres as a chain with different arrangements such as – single sphere; two spheres with equal and unequal sizes; three spheres with equal sizes and multi spheres with different sizes. We analyzed the effect of excitation and polarization with respect to different spheres and position of excitation. We noticed a shift of mode position with respect to different sizes of microspheres. We also had different kind of underlying substrates such as silicon nanopillar, polymer nanopillar, pyramid polymer and nanohole polymer and investigate the effect of these substrates on various chains of microspheres.

Optical resonances in continuous thin films have been under investigation for decades to push the limits of optical components or platforms for sensing or imaging applications. They occur under total internal reflection with the generation of surface plasmons in metallic films or of Bloch surface waves in dielectrics to generate large field enhancements in the near-field of the free interface. I will discuss both situations and give a quick comparison with advantages and drawbacks of both concepts in regard to common applications.

We demonstrate subwavelength scale color pixels in a CMOS compatible platform based on anti-Hermitian metasurfaces. In stark contrast to conventional pixels, spectral filtering is achieved through structural color rather than transmissive filters leading to simultaneously high color purity and quantum efficiency. The subwavelength anti-Hermitian metasurface sensor is able to sort three colors over a 100 nm bandwidth in the visible regime, independently of the polarization of normally-incident light. Furthermore, the quantum yield approaches that of commercial silicon photodiodes, with a responsivity exceeding 0.25 A/W for each channel. Our demonstration opens a new door to subwavelength pixelated CMOS sensors and promises future high-performance optoelectronic systems.

Gaining active, reconfigurable control of optical properties in photonic devices is challenging. Dynamic visible and near-infrared scattering occurs, from cephalopod chromatophore color-producing organs atop iridophores, Bragg stacks consisting of reflectin protein. We present a model, using our broadband refractive indices for xanthommatin, the chromatophore pigment, of the combined chromatophore and iridophore system, a dynamically tunable photonic device in Nature that responds across the visible-near-infrared. We also report on a broadband light-scattering sub-wavelength-periodicity metasurface composed of ferromagnetic islands. This magnetic metasurface is potentially rectifying. By applying a magnetic field, nonlinear optoelectronic properties such as light scattering and optical rectification can be reconfigured. The large tunability of both these electrically- and magnetically-reconfigurable photonic platforms may enable better detectors, new computing architectures, etc.

Thermal detectors are uniquely capable of sensing incident radiation for any electromagnetic frequency; however, the response times of practical devices are typically on the millisecond scale. By integrating a plasmonic metasurface with an aluminium nitride pyroelectric thin film, we demonstrate spectrally selective, room-temperature pyroelectric detectors from 660–2,000 nm with an instrument-limited 1.7 ns full width at half maximum and 700 ps rise time. Heat generated from light absorption diffuses through the subwavelength absorber into the pyroelectric film producing responsivities up to 0.18 V W−1 due to the temperature-dependent spontaneous polarization of the pyroelectric films. This design approach has the potential to realize large-area, inexpensive gigahertz pyroelectric detectors for wavelength-specific detection from the ultraviolet to short-wave infrared or beyond for, for example, high-speed hyperspectral imaging.

In this work, we intentionally explored the heavily p-doped graphene stacks by degenerate femtosecond pump-probe spectroscopy, and observed an excitation enhancement of hot electrons at weak pump fluence. Physically, both Auger processes and population inversion are suppressed in this system, yet it becomes possible for the conduction bands to be effectively evacuated within the pulse duration through the ultrafast cooling of hot electrons, which may lead to an enhanced excitation of hot electrons. This excitation enhancement can be further strengthened by multiple layer-stacking processes or a thermal annealing pretreatment. Furthermore, large modulation depth is achieved in graphene stacks with small variation of pump fluence. We suggest that this effect can have potential applications on harvesting energy from excited hot electrons, and may provide a unique way to achieve high-speed modulators, photodetectors, solar cells, and photocatalysts.

Flexible optoelectronic devices attract considerable attention due to their prominent role in creating novel wearable apparatus for bionics, robotics, health care, and so forth. Although bulk single-crystalline perovskite-based materials are well-recognized for the high photoelectric conversion efficiency than the polycrystalline ones, their stiff and brittle nature unfortunately prohibits their application for flexible devices. Here, we introduce ultrathin single-crystalline perovskite film as the active layer and demonstrate a high-performance flexible photodetector with prevailing bending reliability. With a much reduced thickness of 20 nm, the photodetector made of this ultrathin film can achieve a responsivity much higher than that of recently reported flexible perovskite photodetectors. The demonstrated 0.2 MHz 3 dB bandwidth further paves the way for high-speed photodetection.

Nanostructures store energy differently upon interaction with radiation, depending on the considered time scale, system size, and interacting components. Properly designed nanostructured surfaces confine electromagnetic energy, making it available as high energy electrons and confined fields, far-field scattering, heat or thermal radiation. This talk will show how the spatially inhomogeneous electromagnetic absorption in metallic nanostructures leads to a space-dependent out-of-equilibrium hot carrier population, whose < 1 ps thermalization can be exploited for ultrafast all-optical polarization modulation. Eventually, heat is generated through a slower electron-phonon scattering process. I will show how ultrathin (~250nm) plasmonic metasurfaces can absorb ~90% of the solar spectrum, leading to ~GW/m3 of dissipated power exploited, for example, for steam generation, relevant for sterilization or water desalination applications.

The dynamics of plasmonically induced hot carriers offers a novel route to nonlinear optical effects. In this Keynote lecture, we elucidate how to leverage the generation, transport, and relaxation of hot carriers for externally triggered nonlinear optical properties in nanophotonic structures. Examples to be presented include the ultrafast control of light via hot-electron modulated optical Kerr effect, and ultrafast conversion of a statically-passive dielectric to a transient second-order nonlinear medium upon the creation and transfer of hot carriers. The methodology described here can be extended to various material systems, enabling a new class of “material-by-design” for nonlinear optical effects.

Gauss and convoluted Lorentz-Gauss models make an important class of broadband dispersion formulations for optical materials with structural or molecular disorder, including glasses, polymers, phase change materials, metals. So far, this important class of dispersion models has been inaccessible for time-domain solvers. We suggest a framework to model Gauss-type dispersion in time domain with a given accuracy, based on our previous Generalized Dispersive Material (GDM) model. The new explicit closed-form formulation of Gauss-based models and provided code package give a new physical interpretation in terms of coupled oscillators while also providing an efficient way to its time domain implementation for transient or nonlinear analysis in custom and commercial software.

Graphene’s optical response is characterized by constant absorption in the visible, electrically tunable absorption in the NIR-SWIR and plasmonic excitations in the midIR-LWIR spectrum. These traits make for interesting applications in broadband photodetection. To make the response more efficient we must integrate graphene with resonant photonic or plasmonic cavities. In a comprehensive modeling scheme of graphene-based optoelectronic applications, the optical, thermal, and electrical responses are considered within a self-consistent approach: absorption creates hot carriers, whose temperature distribution is determined by the thermal properties of graphene and the appropriate relaxation pathways and corresponding rates, which are all themselves functions of the temperature. Such a modelling approach will be presented, along with our recent studies on several graphene-based photodetector designs.

Here, we experimentally demonstrate a bendable cloaking structure composed of obliquely stacked planar metallic shells that individually enclose the objects to be hidden. The ensemble of shells acts as a disordered oblique grating that can be bent to form a curved structure; this bendable cloaking structure exhibits broadband invisibility from 0.2 to 1.0 THz, and the curved cloaking structure is functionally effective for incident angles ranging from -10° to 30°. A wide range of practical applications exists that would require hiding cloaked objects with sizes of the order of hundreds of microns, which are smaller than the sizes of the metal shells. In principle, similar cloaking effects can be achieved for a broad bandwidth of frequencies ranging from infrared to radio waves.

Dielectric metamaterials with high refractive indices may have an incredible capability to manipulate the phase, amplitude, and polarization of the incident light. Combining the high refractive index and the excellent electrical characteristics of the hybrid organicinorganic perovskites (HOIPs), we demonstrate that metamaterial made of HOIPs can trap visible light and realize effective photonto-electron conversion. The HOIP metamaterials are fabricated by focused ion beam milling on a solution-grown single-crystalline HOIP film. The optical absorption is significantly enhanced at the visible regime compared to that of the flat HOIP film, which originates from the excited Mie resonances and transverse cavity modes with inhibited interface reflection. Our results point to the potential application of HOIP metamaterials for high-efficiency light trapping and photon-to-electron conversion.

In this work, we show how J-aggregate doped polymers can establish a novel polymer organic active photonic platform for nanophotonics. These polymer materials are able to confine light at nanoscale supporting Surface Exciton Polaritons (SEP) similar to Surface Plasmon Polaritons. This novel organic platform can exploit the fabrication tools of supramolecular chemistry, to control and design J-aggregates which give access to light-confinement at desirable new wavelengths across the visible and near-infrared; extending plasmonics beyond the fixed properties of metals by a new means.

Cadmium Sulphide(CdS) has been the most preferred n-type buffer layer and Indium Tin Oxide(ITO) is the popular window layer in kesterite solar cells. Cadmium being toxic and Indium being a rare earth element, continuous efforts are being made to replace these materials from kesterite solar cells structure. In this work, ZnS, ZnSe, and Zn_0.8Sn_0.2O are considered as possible alternatives for CdS. Similarly, Aluminium doped Zinc Oxide(AZO) is considered as an alternative for ITO. Firstly, a cell model with CdS and ITO (Mo/CZTSSe/CdS/ZnO/ITO) is developed using SCAPS-1D software. To optimise the performance parameters namely open-circuit voltage(Voc), short-circuit current density(Jsc), fill factor(FF), and the power conversion efficiency (PCE) for irradiation under normal working conditions, thickness and the composition ratio of the absorber layer(CZTSSe) are evaluated through numerical simulations. PCE of 14.51% is achieved for a 40% of Sulphur content and 2 um thickness of Cu₂ZnSn(S_xSe_1-x)4 when CdS is used as the buffer layer. For the same structure, replacing ITO with AZO results in a PCE of 14.62%. Use of Cadmium-free buffer layers ZnS, ZnSe, and Zn_0.82Sn_0.18O with ITO as window layer result in PCE of 13.98%, 14.28%, and 14.53%, respectively. For the Cadmium-free buffer layers, an improvement in PCE is achieved when ITO is replaced by AZO, with the highest being 14.62% for Zn_0.82Sn_0.18O. This can be attributed to the smaller conduction band offset, which reduces the recombination of photogenerated carriers and improves the carrier transport in the solar cell. The above results indicate that the Zn_0.8Sn_0.2O and AZO can be potential candidates for the buffer layer and window layer, respectively, for high-performance and cheap kesterite solar cells.

We show that radiation of random fiber Raman laser can be driven into pulsed operation via self-gain-switching. The regime is characterized by small time jitter. We also experimentally demonstrate the self-gain-modulation induced pulsed operation in random fiber laser occurs with switching of repetition rate, that occurs with the increase of the pump power. We present a simple formula that describes possible repetition frequencies.

We directly observe ultra-narrow spectral modes in the generation of the random fiber laser by using a technique of optical heterodyning in real-time. These solitary spectral features appear slightly above the threshold of generation. We found that such modes could have a spectral width well below 3 MHz. These modes are spatially extended over the fiber laser length, and remain for tens of roundtrip times.

In this paper, we present electrically tunable metasurfaces that exhibit multifunctional characteristics in the visible domain by exploiting electro-optic effect (EO). The metasurfaces consist of an array of Barium Titanate (BTO) meta-atoms on an Indium Titanium oxide (ITO) coated substrate. The resonance wavelength of the metasurface can be tuned by varying the electric field that eventually alters the refractive index of material. The tunability of resonance wavelength is evaluated by a hologram that appears at the desired wavelength by changing its voltage. Furthermore, a zoom metalens is presented with focal length shift by applying different electric fields at the wavelengths of 488, 532 and 633 in nm. The proposed idea can be useful for realizing tunable integrated systems.

We introduce a new method to affect the energy cascade through wavevectors accountable for the turbulence. By the introduction of a spatiotemporal non-Hermitian potential we have been able to tilt or promote the energy cascade to reduce or increase turbulence in the universal Complez Ginzburg Landau equation. This is possible thanks to the asymmetric properties of these type of potentials. We show that the most efficient management of the turbulence happens for a phase shift between the real and imaginary part of the modulation different from the one arising from a conventional PT-symmetric theory for transverse potentials. We have been able to physically and analiticaly understand this difference.