This PDF file contains the front matter associated with SPIE Proceedings Volume 12196, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

We demonstrate a nonvolatile electrically programmable phase-change silicon photonic switch and phase shifter leveraging a monolayer graphene heater with record-high programming energy efficiency (8.7±1.4 aJ/nm³) and endurance (> 1,000 cycles).

Topological properties of Bloch modes have been demonstrated in purely dielectric photonic crystals at high symmetry points where a hidden time reversal-like symmetry can be exhibited. So far, the topological properties that have been shown are essentially due to these symmetries. For one dimensional structure, we define a topological invariant that can be extended to lossy or aperiodic structures.

Recently proposed nonvolatile chalcogenide phase change materials Sb₂Se₃ and Sb₂S₃ exhibit low loss and significant refractive index modulation in the visible and NIR, which paves the way for the development of novel reconfigurable on-chip nanophotonic devices and programmable optical devices. Here, we discuss our recent investigations in terms of such devices, in particular, the realization of a compact (3 μm × 3 μm) integrated silicon nanophotonic 1 × 2 optical switch with phase change material Sb₂Se₃, and programmable multilevel diffractive optical lenses and holograms with phase change material Sb₂S₃.

Zoom lenses with adjustable focal lengths and magnification ratios are an crucial part for many optical imaging systems. Conventional zoom lenses comprise multiple refractive optics. Optical zoom is achieved with translational motion of multiple lens elements, which inevitably increases module size, cost, and complexity. Here, we present a zoom lens design based on multi-functional optical metasurfaces. It achieves large zoom ratios with diffraction-limited quality and minimal distortion. Also, it requires no mechanical moving parts. We demonstrate the concept with two embodiments, one in the visible with polarization-multiplexing, and the other in the mid-infrared with phase change materials. Both of them achieve 10x parfocal zoom consistent with the design.

Phase change materials or PCMs are truly remarkable compounds whose unique switchable properties have fueled an explosion of emerging applications in electronics and photonics. Nonetheless, if we discount their use in optical discs, PCMs’ immense application potential in photonics beyond data recording has only begun to unfold in the past decade. While the material requirements for optical or electronic data storage have been succinctly summarized as five key elements “writability, archival storage, erasability, readability, and cyclability” decades ago, these requirements are not universally relevant to the diverse set of photonic applications now being explored. It also comes as no surprise that existing PCMs, which have been heavily vetted for data storage, are not necessarily the optimal compositions for different use cases in optics and photonics. PCMs with their attributes custom-tailored for specific applications are therefore in demand as phase-change photonics continue to expand. Here we discuss the PCM selection and design strategies specifically for photonic applications as well as our recent work developing active integrated photonic devices and meta-surface optics based on new PCMs tailored for photonics.

Phase-change materials (PCMs) integrated photonics are generating new paradigms, thanks to their zero static energy consumption, capability of switching reversibly, and drastic optical property contrast. However, electrically switching PCMs is inherently stochastic, hindering reliable multi-level or quasi-continuous operations. Here we propose that reliable quasi-continuous operation can be achieved in GST optical switches, where several GST patches are controlled in a binary fashion by interleaved PIN-diode doped silicon microheaters. We further experimentally demonstrate that the idea works in a tunable attenuator.

Silicon photonics has emerged as the dominant technology platform for short distance, inter-chip communication for a variety of photonic computing and sensing applications due to its efficiency in modulation and confinement of light across telecom frequencies in addition to its inherent CMOS compatibility. The integration of metallic nanogaps within silicon photonic architectures provides a promising route for scaling this platform through the extreme confinement offered by plasmonics while providing an efficient route to interfacing future photonic integrated circuits with electronics. However, fabricating the gap sizes (< λ_g/10) required of plasmonic resonating nanogaps for efficient operation across telecommunication frequencies is highly challenging. Efficient coupling from waveguides to plasmonic nanogaps also remains a major source of loss. Here, we show that the key to merging these platforms lies in applying metamaterial/metasurface engineering principles to the design of the nanogap. Over the last decade, metamaterials and metasurfaces have emerged as a versatile toolkit for control and enhancement of light-matter interaction at application-driven wavelengths of interest in nanophotonic device platforms. We show that integrating a metagrating within a waveguide-coupled plasmonic nanogap made from Au, can enhance coupling to and from the silicon waveguides. Furthermore, the incorporation of the metasurface within the gap allows resonant response to be maintained at user-specified wavelength of interest with gaps as large as λ_g/5, drastically easing fabrication. Finally, we show that by incorporating a reconfigurable phase change chalcogenide alloy into the gap, non-volatile signal switching with modulation contrasts of up to 10:1 can be achieved across telecom frequencies.

Optical vortices, the spatial modes of an electromagnetic wave carrying orbital angular momentum (OAM), have attracted increasing interest because of their potential for applications in optical communication with enhanced security and channel capacity. A unique optical vortex (OV) generation method has been recently proposed based on the Pancharatnam–Berry (PB) phase induced by the winding topology of polarization around a vortex singularity at bound states in the continuum (BIC). Compared with the recently emergent metasurface-based OV generators, which rely on spatial variations, the BIC-based OV generators have yielded advances in terms of design feasibility, fabrication complexity, and robustness. However, their applications in practical photonic systems are currently limited because OV generations from BIC-related devices originate from the topological property of the photonic bands and cannot be dynamically altered. Here, by leveraging the vortex topology in momentum space together with the nonlinear dynamics of silicon, we demonstrate that a silicon photonic crystal slab can realize optically switchable OV generation. In particular, the spatial tunability and the switching effects in the picosecond scale are studied using nonlinear modeling at near-infrared wavelengths. The demonstrated nontrivial topological nature of the active generators can expand the application of BIC-based devices to include ultrafast vortex beam generation, high-capacity optical communication, and mode-division multiplexing.

While two-dimensional (2D) structural photonic materials have led to many new innovations in the field of optics, the preferential alignment and assembly of colloidal particle arrays over large areas remains a challenge. Here, we develop a theoretical model based on the constructal law in order to describe this particle assembly behavior. The constructal model was then used to predict and tune the resulting particle alignment with and without the presence of an external driving force. Ultimately, this model provides a generalized framework that could be expanded upon to predict the self/directed-assembly of colloidal particles in a range of dynamically tunable and reconfigurable systems.

Magneto-plasmonic nanostructures are multi-functional materials that promise novel applications for the development of surface plasmon resonance (SPR) sensors. This type of structure combines features of ferromagnetic and noble metals, giving magnetic nanoparticles with outstanding optical properties due to the plasmonic response of noble metals. This study is focused on the development of an optical technique based on a total internal reflection configuration with the use of colloidal core-shell nanoparticles for the sensing of organic pollutants in freshwater. Specifically, nanoparticles with a magnetite core and gold shell (Fe₃O₄@Au) are used. These nanostructures allow a spectral tunability of their optical response depending on the geometric features of the nanoparticles such as size or shape. As a result, the localized surface plasmon resonance (LSPR) of these nanoparticles can be fine-tuned over a wide spectral domain. For this purpose, finite-difference time-domain (FDTD) simulations were implemented to guide the nanoparticle synthesis and to be able to compare theoretical and experimental results. The magnetic properties allow the facile collection of the nanoparticles from solution as well as the immobilization and concentration of the nanoparticles in presence of a permanent magnet. Simultaneously, the gold shell of these nanoparticles is optically active, which will enable analyte detection via fluctuations of the reflectance curve which occur when molecules bind to the gold surface.

We introduce a nanoplasmonic isolator consisting of a cavity coupled to a metal-dielectric-metal (MDM) waveguide. The waveguide and cavity are filled with a magneto-optical (MO) material, and the structure is under a static magnetic field. We show that, when MO activity is present, the cavity becomes a traveling wave resonator with unequal decay rates into the forward and backward directions. As a result, the structure operates as an isolator. We also introduce non-Hermitian plasmonic waveguide-cavity systems with topological edge states (TESs) at singular points. The structure unit cells consist of an 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 such structures achieve extremely high sensitivity of the reflected light intensity. TESs at singular points could lead to singularity-based plasmonic devices with enhanced performance.

We model the effect of concentrated sunlight on CIGS thin-film graded-bandgap solar cells using an optoelectronic numerical model. For this purpose it is necessary first to solve the time-harmonic Maxwell equations to compute the electric field in the device due to sunlight and so obtain the electron-hole-pair generation rate. The generation rate is then used as input to a drift-diffusion model governing the flow of electrons and holes in the semiconductor components that predicts the current generated. The optical submodel is linear; however, the electrical submodel is nonlinear. Because the Shockley-Read-Hall contribution to the electron-hole recombination rate increases almost linearly at high electron/hole densities, the efficiency of the solar cell can improve with sunlight concentration. This is illustrated via a numerical study.

We apply the Stimulated Emission Tomography (SET) technique to assess the ability of plasmonic nanoantennas to generate correlated photon pairs via spontaneous four-wave mixing (SFWM). In line with SET theory, we characterize the SFWM pair generation rate by studying the case of stimulated four-wave mixing (FWM). By calculating the number of stimulating and generated photons along with the frequency mixing efficiency, we estimate the SFWM pair generation rate. We also produce a map of the joint spectral density (JSD) to characterize the bi-photon state with greater resolution than that of spectrally resolved coincidence measurements.

Silicon photonics has matured over the last decade as a unique platform for highly miniaturized photonic integrated systems seamlessly integrated with electronics allowing the realization and commercialization of highly compact devices with ultrafast data transfer rates and significantly reduced power consumption. Although such submicron scale photonic and waveguide structures enable dense on-chip device integration, they also result in reduced efficiency in fiber-to-waveguide coupling mainly due to increased mode area mismatch. As a result, one of the key challenges faced in current technology platforms has been to efficiently couple light without additional fabrication, post-processing, and complex optical alignment. In-plane grating couplers (GC) have been a widely preferred coupling platform, mainly because of low fabrication costs, ease of alignment and high-level of flexibility in circuit design. A wide range of coupling platform designs have been investigated in the last decade including both passive and active designs. In passive design the coupling efficiency (CE) is fixed once the device is fabricated, however in active designs various tuning mechanism have been explored to modulate the CE, but at the expense of increased power consumption and reduced CE. Using inverse design techniques, we demonstrate CMOS compatible, reconfigurable phase change chalcogenide-on-insulator based apodised GC having maximized CE of more than 50% at λ=1550nm when the phase of the chalcogenide is in amorphous state. When the phase is switched to crystalline state, a near zero CE is shown allowing the design to be both non-volatile and reversibly reconfigurable with highest transmission modulation contrast of more than 50db.

This work considers the advantages and drawbacks of fibre-optical platforms as used for development of short-pulsed light sources and experimental research installations. Solutions are analysed, which enable active, dynamic, and tuneable control of light. A unique combination of conditions — medium dispersion, nonlinearity, and radiation spectral range — gives rise to new states of light, interesting both scientifically and practically. The prospects of the fibre-optical platforms for development of next-generation lasers and research equipment are discussed.

Kesterite solar cells require a novel high-research implementation to replace the costlier Copper Indium Gallium Selenide (CIGS) solar cells. This study, attempts to demonstrate the performance improvement of kesterite solar cells using multiple quantum wells (MQWs). A numerical simulation approach using Atlas software from Silvaco is used. Firstly, a baseline model of the best performing Cu₂ZnSnS₄(CZTS) solar cell Mo/CZTS/CdS/i-ZnO/ITO with 11% power conversion efficiency (PCE) is implemented. Further, to exploit the use of MQWs, Cu₂ZnSn(S_xSe_1-x)₄ (CZTSSe) with 40% sulfur content is added as well material in a series of wells while keeping the CZTS as the barrier material. This structural modification facilitates the absorption of lower energy photons by the lower bandgap well material. Further, MQW induced quantized energy levels and higher electric fields help to increase the carrier collection, thereby increasing the solar cell's short circuit current density (Jsc) and overall power conversion efficiency (PCE). A detailed study on the effect of well and barrier thickness on the solar cell performance is done, and a well thickness of 5 nm and a barrier thickness of 10 nm was chosen for further optimization. The number of wells is also optimized to 70, which results in the highest performance of the solar cell. This structural modification and optimization remarkably improved Jsc by 48.76% (rel.) and PCE by 34.72% (rel.) compared to solar cells without nanostructures. Moreover, with an optimized structure, an external quantum efficiency (EQE) of over 95% is achieved with the optimized structure.