This PDF file contains the front matter associated with SPIE Proceedings Volume 12647, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Photonic platforms are envisioned to play a pivotal role across various domains including information processing and towards the development of next generation of quantum technologies. Atomically thin semiconductors are a promising ingredient for combination with photonic structures as they provide strong light-matter interaction and inherent spin-valley locking of excitons generated with different circularly polarized light. In this work, we show two different applications of two-dimensional transition-metal dichalcogenides. First, we demonstrate a chiral metasurface that allows reflection of selective polarization of light within a narrow spectral band utilizing the valleytronic properties. Second, we propose electro-optic phase modulators based on monolayer semiconductors for integration in large-scale photonic circuits.

Photonic neuro-transistors that utilize the persistent photoconductivity behavior by heterojunction structures has been previously used for light-driven synaptic performance. By varying the anion-to-cation ratio of the light-absorbing layer and the semiconductor, the photonic transistors were able to precisely mediate the degree of energy band-bending at the heterointerface, leading to efficient accumulation of photo-generated charge carriers and the emulation of biological synaptic functions. The photonic neuro-transistor with the optimized structure achieved a high ratio of effective conductance-level states for both long-term potentiation and long-term depression, along with linear conductance change and less energy consumption compared to previously reported optoelectronic neuromorphic devices. Deep spike synaptic transistor with deep level potential well enables linear conductance change with low non-linearity values (NL) of 1.1 during long-term potentiation (LTP) behaviors along with low energy consumption (45.04 pJ). We also demonstrate the feasibility of large-area optoelectronic neuromorphic arrays and explore training and inference tasks simulation using Modified National Institute of Standards and Technology (MNIST) data set, achieving high recognition accuracy of 85.96% . This study shows potential for the development of energy-efficient neuromorphic computing systems for artificial intelligence applications.

The high demand for AI services in conjunction with a dramatic chip shortage along with technology leaps such as 5/6G networks, quantum technologies, cybersecurity threats, and the CHIPS Act have resurrected a R&D push for next-generation semiconductor materials, devices, and information processing hardware capability. In this paper, we will present the latest advances in regarding programable photonics and chip, from devices to packaging and system architecture, bringing these innovations into the bigger picture of macro trends and national priorities such as Industry-4.0 and the recent U.S. CHIPS Act.

The past decade has witnessed a surge of interest in the theory and application of time-varying components in engineered photonic and electromagnetic structures. While time-varying photonic materials have been shown to enable novel and unique physical phenomena, many of these research efforts have been additionally motivated by the desire to overcome various performance limits related to, for instance, antenna radiation, absorption, and impedance matching. Given that many physical limits in electromagnetism/photonics are typically derived under the assumption of passivity and time-invariance, judicious time-varying designs may challenge and overcome these limitations. In this context, the most common design strategy involves employing a time-switched material, where one or more of the constitutive parameters undergo abrupt changes in time. Although this approach offers promising results, its implementation poses significant challenges. Specifically, complex synchronization mechanisms are necessary to accurately time the switching of the material parameters with respect to the arrival time of the pulse. Additionally, the switching event usually needs to take place when the pulse is entirely contained within the medium, leading to a potential constraint on the minimum thickness of the time-varying system. Here, we show that, instead of a time-switched material, certain periodically modulated time-Floquet systems can significantly enhance the absorption bandwidth and can even go beyond the conventional bounds of a thin absorber without prior knowledge of the arrival time of the pulse. Our findings may open a new route in the design of time-varying systems that are not bound by conventional performance limits and may facilitate their implementations.

Space-time metasurfaces are great candidates for breaking the Lorentz reciprocity thorough inducing the desired momentum for photonic transitions between two modes. However, the significant difference between the carrier and modulation frequencies in photonic metasurfaces leads to negligible spatial pathway variation of light at different sidebands and weak power isolation. To surmount this obstacle, herein the design principle of the high Q-factor space-time metasurface is demonstrated that increases the lifetime of photons such that the optical cycle becomes comparable with the modulation cycle and strong power isolation is maintained by lifting the adiabaticity of modulation. It is shown that under time-reversal and by the virtue of modulation induced phase shift strong free space power isolation of ≈35dB is achieved between the two arbitrary ports at near-infrared regime.

We introduce non-Hermitian plasmonic waveguide-cavity structures based on the Aubry-Andre-Harper model to realize switching between right and left topological edge states using the phase-change material germanium-antimony- tellurium (GST). The structure unit cells consist of a metal-dielectric-metal (MDM) waveguide side-coupled to MDM stub resonators with modulated distances between adjacent stubs. In such structures the modulated distances introduce an effective gauge magnetic field. We show that switching between the crystalline and amorphous phases of GST leads to a shift of the dispersion relation of the optimized structure so that a right topological edge state for the crystalline phase, and a left topological edge state for the amorphous phase occur at the same frequency. Thus, we realize switching between right and left topological edge states at that frequency by switching between the crystalline and amorphous phases of GST. Our results could be potentially important for developing compact reconfigurable topological photonic devices.

Photonic modulators have seen widespread use in optical circuitry, optical processing, and next-generational computing regimes such as neuromorphic computing. Prior research has focused on the incorporation of high-index functional materials on or adjacent to photonic circuit components such as modulators to enhance signal detection, modulation, and generation. The reversible, non-volatile transitions between optically and electrically unique amorphous and crystalline material phases inherent to chalcogenide phase-change materials (PCMs) present a promising material platform for this integration. However, current methods of incorporation combined with lossy material properties lead to integrations having large insertion losses and device footprints. Here we demonstrate that applying metamaterial effective medium theory enables dispersive engineering to drastically reduce insertion losses and footprints in PCM-loaded optical circuitry. Two configurations are explored, a metagrating and a multilayer, in which full-π modulator phase shifts are achieved in compact footprints down to 4.36 and 4.7 𝜇m with low insertion losses at a 1550nm wavelength.

New photonic devices such a metamaterials and meta surfaces are made of a large number of scattering elements strongly interacting. The modeling of these structures requires handling many degrees of freedom that can become prohibitive in terms of computing capacities. In this work we propose to define a new mathematical object that we call the ”holographic scattering matrix”. It allows to describe a cluster of scatterers by an operator defined on the boundary of a surface enclosing the scatterers. Elements with gain or loss can be handled. This allows to generalize the so-called Fast Multipole Algorithm to go beyond the spherical harmonics.

We show that Skyrmions provide a natural language and tool with which to describe and model structured light fields. These fields are characterised by an engineered spatial variation of the optical field amplitude, phase and polarisation. In this short presentation there is scope only for dealing with the simplest (and perhaps most significant) of these namely those that can be designed and propagate within the regime of paraxial optics. Paraxial Skyrmions are most readily defined in terms of the normalised Stokes parameters and as such are properties of the local polarisation at any given point in the structured light beam. They are also topological entities and as such are robust against perturbations. We outline briefly how Skyrmionic beams have been generated to order in the laboratory. Optics gives us access, also, to the Skyrmion field and we present the key properties of this field and show how it provides the natural way to describe the polarisation of structured light beams.

Optical vortices are beams of laser light in which photons are conveyed with a helical wavefront. With a corresponding azimuthal dependence in optical phase, their screw symmetry supports orbital angular momentum, strongly contrasting with the more familiar and quantitatively limited quantum spin. The study and methods of production of these beams now represent rapidly accelerating areas in optical physics and technology, driven by applications that include novel forms of interaction with structured matter. Conventional measures of optical helicity, usually associated with circular polarizations, are not suited to determining the mechanisms that underpin such optical vortex interactions. It is therefore of great interest to identify and characterize the symmetry aspects of the quantized fields of vortex radiation that relate to the beam, and which become manifest in these interactions. Despite the absence of most physical, 3D structural symmetry elements in chiral matter, careful consideration of fundamental charge-parity-time symmetry delivers key insights; duality symmetry between electric and magnetic fields is also involved. A photon-based analysis of such features reveals key features of significance for the nanoscale interactions of vortex beams, indicating new scope for suitably tailored experimental design.

We investigate the effect of fabrication tolerances on photonic multimode waveguides operating in the vicinity of a third-order exceptional point degeneracy (EPD), known as a stationary inflection point (SIP). An EPD is a point in the parameter space where two or more Bloch eigenmodes coalesce in an infinite periodic waveguide, and at an SIP three modes coalesce to form the frozen mode. Waveguides operating near an SIP exhibit slow-light behavior in finite-length waveguides with anomalous cubic scaling of the group delay with waveguide length. The frozen mode facilitates stronger light-matter interactions in active media, resulting in a significant increase in the effective gain within the cavity. However, systems operating near an EPD are also exceptionally sensitive to fabrication deviations. In this work, we explore wave propagation and the impact of various fabrication imperfections in analytic models and in fabricated photonic chips for three mirrorless devices operating near an SIP. To advance the concept of the SIP laser, we also analyze how the addition of gain and loss affects the SIP performance. Our results show that while minor deviations from the ideal parameters can prevent perfect mode coalescence at the EPD, the frozen mode remains resilient to small perturbations and a significant degree of mode degeneracy prevails. These findings provide critical insights into the design and fabrication of passive and active photonic devices operating near high-order EPDs, paving the way for their practical implementation in a wide range of applications.

We demonstrate circularly-polarized-like modes with maximum chirality at the exceptional point (EP) of a photonic crystal (PhC) defect cavity. Reaching the EP requires a fine balance between the loss/gain and dielectric perturbation and a high consistency between fabrications and designs. In this work, we use the tunneling loss that can be controlled by the number of removed air holes in the PhC to induce the EP. By removing and repositioning the hole blocks, we make the EP insensitive to uncertainties in fabrications and improve the chirality of radiation field. Our results promote coherent chiral light sources at the chip level without auxiliary non-Hermitian and chiral structures.

The FDTD numerical simulations are used to investigate the time evolution of the two-level system of conduction and valence bands. Free carriers’ population dynamics in the conduction band for large intensities of the ultrashort pulse (100 fs) is calculated. The results show that time-dependent real part of the optical permittivity at ENZ spectral point is saturated and resembles a step function as the ultrashort pulse amplitude reaches ~10¹⁰ V/m. The calculated value of the intensity-dependent refractive index is n₂~-2×10^-11 cm²/W. The results demonstrate that increasing initial carrier concentration from ~2×10²⁰cm^-3 to ~4×10²⁰cm^-3 leads to a significant n₂ magnitude change.

Dielectric nanostructures are cherished because of their great potential for low-loss optical devices. Achieving strong optical resonances in dielectric nanostructures is the key to realizing practical dielectric metadevices. In particular, the exploration of new mechanisms for high quality (Q) factor resonances in dielectric architectures provides the basis for actively tunable responses and nonlinearities. In this work, we study the switchable optical responses from dielectric/plasmonic hybrid systems and the nonlinearities in pure dielectric nanostructures supporting optical resonances associated with the bound states in the continuum (BICs). First, we show that, under optical excitations, hybrid metasurfaces based on a dielectric nanoantenna array of active materials (such as silicon (Si) and zinc oxide (ZnO)) on a plasmonic (e.g., silver (Ag)) backplane exhibit broadly tunable topological properties. Accordingly, enormously strong polarization manipulation of near-infrared light in the vicinity of the topological features is observed. Second, we study the efficient second harmonic generation (SHG) from asymmetric lithium niobate (LN) metasurfaces. Third, based on the large Kerr nonlinearities of silicon, we explore the nonlinear chiroptical response from a planar Si metasurface supporting high Q-factor guided mode resonances (GMRs) at near-infrared wavelengths. Fourth, leveraging the momentum-space polarization vortices observed in photonic structures, we investigate the switchable and nonlinear optical vortex generation from Si photonic crystal slabs. Our work shows that dielectric nanostructures which support high-Q resonances via careful nanoengineering can serve as a transformative platform for active and nonlinear photonics.

Sum frequency generation is the process in which two incoming photons are converted into an outgoing photon of higher energy. This process is highly inefficient, and therefore requires either large interaction distances in bulky crystals, or large field concentrations in the non-linear materials. Metasurfaces are one such platform to generate extreme field enhancements with resonant processes. In this work, we use topology optimisation to design metasurfaces that exhibit increase high efficiency sum frequency generation, as well as the ability to tailor the generated polarisation.

Electrical system monitoring applications are of increasing importance given recent trends towards electrification driving adoption of renewables and electric vehicles, for example. Thermal and acoustic signatures play an important role in health monitoring while electrical and magnetic field signatures can provide information about operational state. Optical fiber sensors are of particular interest for electrical system applications because of the compatibility with deployment in electrified systems without concerns for electromagnetic interference (EMI) or additional potential risks due to the presence of electrical sensor wires or power at the sensing location, particularly for medium voltage electrical systems. In this presentation, an overview of recent work in optical fiber-based sensing for electrical asset monitoring applications will be discussed in detail. Plasmonic sensors integrated with engineered nanomaterials will be discussed for thermal and other health monitoring applications while interferometric sensors will be discussed for acoustics and also magnetic fields and electrical current sensing. New directions in fiber-based sensing applications will also be discussed moving into the future.

Neuromorphic vision sensors aim to replicate the human visual system by transforming light into electrical signals. However, achieving color discrimination remains a challenge. Colloidal quantum dots (QDs) are being investigated as photoactive materials for artificial synaptic applications. QD-based phototransistors have shown promise for their versatile photo-synaptic memory behaviors and neuromorphic image processing capabilities. This study proposes incorporating a mixed-QD system of different sizes within a single device to improve color identification and spatio-temporal resolution. An amorphous In-Ga-Zn-O (IGZO) thin-film transistor amplifies the signals, and a heterojunction between absorption and channel layers achieves synaptic function by storing charges, enabling the device to recognize and distinguish light signals of varying wavelengths and intensities.

Plasmonic metal-oxide metastructures comprise arrays of Au nanoantennas embedded in Si layers, with a top ultrathin layer of Al oxide, supporting an Au/Si Schottky junction in the vicinity of a Si/Al oxide charge barrier. In such structures the hot electrons generated by nonradiative decay of plasmons can be captured by the Schottky junctions, forming an electrostatic field via charge accumulation in the Si layers. When thin layers of semiconductor quantum dots are placed on top of such structures, such a field suppresses their non-radiative decay rates, making them far more efficient emitters. We study the impact of plasmon modes of the Au nanoantennas on the exciton-plasmon coupling enhancement supported by such a material platform.

Using carefully arranged electric and magnetic components, we have recently demonstrated that backscattering from otherwise arbitrarily shaped two- and three-dimensional structures can be fully eliminated. Here, first we investigate the possibility of creating self-dual microwave absorbers that may provide advantages compared to typical commercial magnetoelectric absorbers. Next, we demonstrate that the self-duality condition is not limited to homogenous structures and may be extended to effective material properties, opening the door to realistic implementation of these structures at microwave and optical frequencies.

We initially developed an efficient solver to study photodetectors composed of multiple semiconductor layers with varying thicknesses and doping concentrations. Subsequently, we employed it as the forward solver for three different numerical optimization methods aimed at designing Si-Ge photodetectors with larger bandwidth, higher quantum efficiency, and lower phase noise. Our work offers new insights into the design of high-performance photodetectors—a challenging task due to computation time, design constraints, and the complexity of estimating sensitivity to design parameters.

We introduce multilayer structures with the phase-change material germanium-antimony-tellurium (GST) for use as broadband switchable absorbers in the infrared wavelength range. We use a memetic optimization algorithm coupled with the transfer-matrix method to optimize both the material composition and the layer thicknesses of the multilayer structures. We show that in the optimized structures near perfect absorption can be switched to very low absorption in a broad wavelength range by switching GST from its crystalline to its amorphous phase. Our results could pave the way to a new class of broadband switchable absorbers and thermal sources in the infrared wavelength range.