We present a scalable approach capable of manufacturing high-precision three-dimensional (3-D) GRIN nanocomposites based on multi-component bulk glass-ceramics where we spatially modulate the concentration of high refractive index nanocrystals within a glass matrix. Previously demonstrated in homogeneous thin films and bulk glasses containing large scale liquid-liquid phase separation, this work expands on our efforts to optimize processing protocols employing a near single-phase bulk glass starting material enabling true 3-D modification. Sub-bandgap laser exposure generates Pb-rich amorphous phases within a Ge-As-Pb-Se glass matrix, which undergo crystallization resulting in the formation of highindex nanocrystals upon controlled heat treatment. Nanocrystal density is modulated in both radial and axial geometries by the laser dose, providing spatially tailorable changes in index and dispersion.
Chalcogenide phase change materials (PCMs) are a unique class of compounds whose switchable optical and electronic properties have fueled an explosion of emerging applications in microelectronics and microphotonics. The key to any application is the ability of PCMs to reliably switch between crystalline and amorphous states over a large number of cycles. While this issue has been extensively studied in the case of microelectronic memories, current PCM-based optical devices suffer from much inferior endurance. To understand the failure mechanisms limiting endurance of PCMs specifically in microphotonic devices, we have developed an on-chip resistive micro-heater platform and an automatic multi-modal characterization system to analyze cycling performance of optical PCMs. Reversible switching of large-area PCM devices over 50,000 cycles was demonstrated.
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.
Chalcogenide phase change materials (PCMs) are a class of alloys exhibiting gigantic optical property contrast upon structural transition from an amorphous to a crystalline state. The structural transition is also nonvolatile and does not require constant power supply to maintain its optical state. These unique behaviors qualify PCMs as a novel functional material enabling various on-chip and free-space re-programmable optical computing network architectures. Here we present monolithic integration of PCMs with integrated photonics and metasurface optics leveraging standard silicon foundry facilities, and the demonstration of electrically programmable photonic devices for on-chip optical routing, memory, and computing functions
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 discuss several recent advances in the development of methodologies and techniques used to structurally and morphologically engineer chalcogenide (ChG) materials. We introduce two ChG patterning techniques both offering spatial resolution beyond the classical single-photon diffraction limit: multiphoton lithography and thermal scanning probe lithography (TSPL). The former was applied to produce nanoscale modifications in thermally deposited As2S3, and we realized gradient refractive index (GRIN) effective medium lens fabrication in multilayer As2S3-As2Se3 films with features as small as 120 nm using this approach. The GRIN lens was shown to be optically functional. ChG Ge-Sb-Se-Te (GSST) material was also explored for its potential as a phase-change material (PCM). We demonstrated nanoscale feature patterning using TSPL in PCMs with critical dimensions below 100 nm. In addition, new patterning methods, we also report solution processing of GSST PCMs as an alternative route for ChG film deposition. These new material processing and structuring techniques will offer new pathways for creating functional planar optical and photonic devices.
Optical metasurfaces, planar sub-wavelength nano-antenna arrays with the singular ability to sculpt wave front in almost arbitrary manners, are poised to become a powerful tool enabling compact and high-performance optics with novel functionalities. A particularly intriguing research direction within this field is active metasurfaces, whose optical response can be dynamically tuned post-fabrication, thus allowing a plurality of applications unattainable with traditional bulk optics. The efforts to date, however, still face major performance limitations in tuning range, optical quality, and efficiency especially for non-mechanical actuation mechanisms. In this paper, we introduce an active metasurface platform combining phase tuning covering the full 2π range and diffraction-limited performance using an all-dielectric, low-loss architecture based on optical phase change materials (O-PCMs). We present a generic design principle enabling binary switching of metasurfaces between arbitrary phase profiles. We implement the approach to realize a high-performance varifocal metalens. The metalens is constructed using Ge2Sb2Se4Te1 (GSST), an O-PCM with a large refractive index contrast and unique broadband low-loss characteristics in both amorphous and crystalline states. The reconfigurable metalens features focusing efficiencies above 20% at both states for linearly polarized light and a record large switching contrast ratio (CR) close to 30 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents the first experimental demonstration of a non-mechanical active metalens with diffraction-limited performance.
Optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. The University of Central Florida’s Glass Processing and Characterization Laboratory, together with our collaborators, have been evaluating compositional design and processing protocols for both bulk and film strategies employing multicomponent chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. We review progress in forming ChG-based gradient refractive index (GRIN) materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and metalens structures realized through multiphoton lithography. We discussed current design and metrology tools that lend critical information to material design efforts to realize next-generation IR GRIN media for bulk or film applications.
The dramatic optical property change of optical phase change materials (O-PCMs) allows the realization of tunable optical and photonic devices with enhanced optical functionalities, such as reconfigurable optics, optical switches and routers, and photonic memories. Recently we developed a new class of non-volatile O-PCM, Ge-Sb-Se-Te (GSST), which features unprecedented broadband optical transparency (1-18.5 micron), large optical contrast (dn = 2) and significantly improved glass forming ability. Leveraging the remarkable material property and advanced design methods, we develop a suite of reconfigurable, all-dielectric metasurface optics with unprecedented performance. In one example, a focal length tunable transmissive metalens is demonstrated showing diffraction-limited imaging performance and complete optical function switching during the phase transition, which sets the foundation for ultra-compact, solid-state, tunable meta-optical systems.
The development of low-loss optical phase change materials (O-PCMs) promises to enable a plethora of nonvolatile integrated photonic applications. However, the relatively large optical constants change between different states of calls for a set of new design rationales. Here we report a non-perturbative design that enables low-loss device operation beyond the traditional figure-of-merit limit. The basic design rationale is to engineer the light propagation path through the OPCMs when it is in the low-loss amorphous state, and divert light away from the lossy crystalline state leveraging the large mode modification induced by the O-PCM phase transition. Following this approach, we demonstrate broadband photonic switches with significantly enhanced performances compared to current state-of-the-art.
We demonstrate a scalable photo-thermal process which enables manufacturing of infrared (IR) transmissive glass-ceramic films with gradient refractive index (GRIN) profiles. Spatiallycontrolled laser irradiation creates Pb-rich amorphous phases within Ge-As-Pb-Se glass films, which are subsequently crystallized and become high index phases upon heat treatment. The density of the high index nanocrystals is shown to be controlled by the laser irradiation power, and the extent of fraction crystallized is controlled by post heat treatment time and temperature. Both of these variables can be optimized to realize a localized effective refractive index change, enabling a spatially-modulated refractive index change up to ~ +0.1. We demonstrate IR GRIN functionality within 1 inch diameter GAP-Se films with thicknesses ranging from 1 to 40 μm, confirming the scalability of our photo-thermal process to component-relevant geometries.
Optical phase change materials (O-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. Traditional O-PCMs suffer from large optical losses even in their dielectric states, which fundamentally limits the performance of optical devices based on the materials. To resolve the issue, we have recently demonstrated a new O-PCM Ge-Sb-Se-Te (GSST) with broadband low loss characteristics. In this talk, we will review an array of reconfigurable photonic devices enabled by the low-loss O-PCM, including nonvolatile waveguide switches with unprecedented low-loss and high-contrast performance, free-space light modulators, bi-stable reconfigurable metasurfaces, and transient couplers facilitating waferscale device probing and characterizations.
The ability to employ spatially-selective control of refractive index and dispersion variation with a high magnitude of change is essential for the realization of functional infrared graded-index (GRIN) components. Thin films fabricated from multi-component GAP-Se glass-ceramic materials were processed using nanosecond laser radiation at the wavelength λ = 2 μm. Various irradiation and post-processing protocols were implemented to maximize the magnitude of the local refractive index change, and to quantify the evolution of the glass to glass ceramic ‘conversion’ on optical material physical properties. Irradiation of films possessing various thicknesses from 1 to 25 μm was performed using area-scan patterns, while the average laser power and the number of scans were varied. Irradiated materials were subsequently heat-treated, and the local refractive index was determined for different durations of the heat treatment. Depth-dependent composition and film morphology characterization of as-deposited films was evaluated, and surface morphology of the post laserprocessed and heat-treated areas was studied to evaluate effects on the photo-thermal refractive index change associated with nanocrystal formation. Initial studies demonstrated a maximum positive refractive index change of ▵n ≈ 0.07 in a broad spectral range in the infrared which scales with film thickness and exposure dose while maintaining required optical quality.
The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonic devices with enhanced optical functionalities and low power consumption, such as reconfigurable optical components, optical switches and routers, and photonic memories. Conventional O-PCMs exhibit considerable optical losses, limiting their optical performance as well as application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel meta-optic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to the LWIR. A drastic refractive index change between the amorphous and crystalline states of GSST is realized and the transition is non-volatile and reversible.
Optical metasurfaces consist of optically-thin, subwavelength meta-atom arrays which allow arbitrary manipulation of the wavefront of light. Capitalizing on the dramatically-enhanced optical performance of GSST, transparent and ultra-thin reconfigurable meta-optics in mid-infrared are demonstrated. In one example, GSST-based all-dielectric nano-antennae are used as the fundamental building blocks for meta-optic components. Tunable and switchable metasurface devices are developed, taking advantage of the materials phase changing properties.
The dramatic optical property change of optical phase change materials (O-PCMs) between their amorphous and crystalline states potentially allows the realization of reconfigurable photonics devices with low power consumption, such as optical switches and routers, reconfigurable meta-optics, displays, and photonic memories. However, conventional O-PCMs, such as VO2 and Ge2Sb2Te5, are inherently plagued by their excessive optical losses even in dielectric states, limiting their optical performance and hence application space. In this talk, we present the development of a new group of O-PCMs and their implementations in novel photonic devices. Ge-Sb-Se-Te (GSST), obtained by partially substituting Te with Se in traditional GST alloys, feature unprecedented broadband optical transparency covering the telecommunication bands to LWIR. Capitalizing on the dramatically-enhanced optical performance, novel non-volatile, reconfigurable on-chip photonics devices and architectures are demonstrated. GSST-integrated Si photonics based on the material innovation and novel “non-perturbative” designs exhibit significantly improved switching performance over state-of-the-art GST-based approaches. The technology is further scalable to realize non-blocking matrix switches with arbitrary network complexity, paving the path towards high performance reconfigurable photonics chips.
Novel optical materials capable of advanced functionality in the infrared will enable optical designs that can offer lightweight or small footprint solutions in both planar and bulk optical systems. UCF’s Glass Processing and Characterization Laboratory (GPCL) with our collaborators have been evaluating compositional design and processing protocols for both bulk and film strategies employing multi-component chalcogenide glasses (ChGs). These materials can be processed with broad compositional flexibility that allows tailoring of their transmission window, physical and optical properties, which allows them to be engineered for compatibility with other homogeneous amorphous or crystalline optical components. This paper reviews progress in forming ChG-based GRIN materials from diverse processing methodologies, including solution-derived ChG layers, poled ChGs with gradient compositional and surface reactivity behavior, nanocomposite bulk ChGs and glass ceramics, and meta-lens structures realized through multiphoton lithography (MPL).
Transparent ZnO–Bi2O3–B2O3 (ZBB) glasses were prepared using the melt quench technique. Various compositions of the glass containing stoichiometric ratios of Zn/Bi/B as well as some including As2O3 for redox control and LiNO3 for use as nucleation species, were studied. ZBB glass-ceramics containing nanocrystallites have a potential for use as low-cost UV-MWIR optical devices such as microlenses, waveguides, and photonic crystals. Our goal was to exploit crystal growth in the ZBB systems by heat treatment in order to obtain transparent glass-ceramics that contain homogenous volume crystallization. Thermal behavior was studied using differential scanning calorimeter (DSC) measurements. Physical and optical characterizations included Raman spectroscopy to identify molecular connectivity, energy-dispersive X-ray spectroscopy (EDX) for elemental analysis, VIS/NIR transmission and reflection spectroscopy for optical bandgap and IR transmissivity, X-ray diffraction (XRD) to determine crystal phase, and transmission electron microscopy (TEM) combined with selected area electron diffraction (SAED) to quantify size, number density, and identification of nanometer sized secondary phases. Heat treatments were used to nucleate and grow BiB3O6 and Bi2ZnB2O7 nanocrystals in ZBB. We explored new compositions within the ZBB system and heat treatment techniques to assess the transformation of the amorphous glass phase into the crystalline phase. In-situ XRD and TEM imaging was employed to correlate nucleation temperature, heat treatment temperature, and heat treatment duration with induced crystal phase. BiB3O6, Bi2ZnB2O7, and ZnO was found to grow on the surface of some compositions. Compositions and heat treatment procedures were developed to facilitate volume crystallization and reduce unwanted surface crystallization.
Optical phase change materials (O-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. These materials, exemplified by Mott insulators such as VO2 and chalcogenide compounds, have been exploited for a plethora of emerging applications including optical switching, photonic memories, reconfigurable metasurfaces, and non-volatile display. These traditional phase change materials, however, generally suffer from large optical losses even in their dielectric states, which fundamentally limits the performance of optical devices based on traditional O-PCMs. In this talk, we will discuss our progress in developing O-PCMs with unprecedented broadband low optical loss and their applications in novel photonic systems, such as high-contrast switches and routers towards a reconfigurable optical chip.
Advanced photonic devices require novel optical materials that serve specified optical function but also possess
attributes which can be tailored to accommodate specific optical design, manufacturing or component/device
integration constraints. Multi-component chalcogenide glass (ChG) materials have been developed which exhibit
broad spectral transparency with a range of physical properties that can be tuned to vary with composition, material
microstructure and form. Specific tradeoffs that highlight the impact of material morphology and optical properties
including transmission, loss and refractive index, are presented. This paper reports property evolution in a
representative 20 GeSe2-60 As2Se3-20 PbSe glass material including a demonstration of a 1D GRIN profile through
the use of controlled crystallization.
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