In this work, we introduce actively tunable PCM-FP (Fabry-Perot) and PCM-PNA (Plasmonic Nanohole Array) bandpass filters that possess high-speed tunability (MHz), narrow spectral bandwidth, high-transmissivity, broad tuning range, in an all solid-state design in a wide variety of imaging and spectroscopic applications. We also present the results from a Materials International Space Station Experiment (MISSE-14) in which chalcogenide phase change material (PCM) optical components are exposed and tested in Low Earth Orbit to determine their suitability for space applications. Our samples including Ge2Sb2Te5, Ge2Sb2Se4Te1, Sb2S3 thin-films and PCM-FP were delivered aboard the ISS by Northrop Grumman (NG-15) in Feb. 2021 for 6 months of exposure testing, including: temperature, vacuum, atomic oxygen, UV exposure and solar illumination effects. Our MISSE-14 PCM study will provide valuable information on the limitations and suitability of PCMs in harsh space environments.
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 metasurfaces consist of nanostructured meta-atom arrays that allow on-demand manipulation of the phase, amplitude and polarization of light. The promise of metasurface optics lies in the arbitrary wavefront control with an optically-thin, flat/conformal form factor and subwavelength-arrayed device architecture, in drastic contrast to traditional bulk optics. In this talk, we’ll discuss opportunities and challenges of using metasurfaces in imaging systems. We further present novel imaging optics and architectures enabled by ultra-thin, all-dielectric metasurfaces, such as ultra-wide field-of-view and reconfigurable meta-optics with unprecedented optical performance. We show that the judicially-engineered meta-optics can significantly boost the imaging performance, allow new functionalities and effectively reduce the size, weight, power and cost (SWaP-C) of future optical systems.
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.
On-chip optical isolators constitute an essential building block for photonic integrated circuits. Monolithic magnetooptical isolators on silicon, while featuring unique benefits such as scalable integration and processing, fully passive operation, large dynamic range, and simple device architecture, had been limited by their far inferior performances compared to their bulk counterparts. Here we discuss our recent work combining garnet material development and isolator device design innovation, which leads to a monolithic optical isolator with an unprecedented low insertion loss of 3 dB and an isolation ratio up to 40 dB. To further overcome the bandwidth and polarization limitations, we demonstrated broadband optical isolators capable of operating for both TM and TE modes. These results open up exciting opportunities for scalable integration of nonreciprocal optical devices with chip-scale photonic circuits.
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 have already successfully employed the Generalized Dispersion Material (GDM) technique to include optical dispersion of different materials in the multiphysics time domain methods implementing the GDM model with various Auxiliary Differential Equation (ADE) and Recursive Convolution (RC) schemes. So far, we have demonstrated that the approach works efficiently to model the optical dispersion of metals, and to characterize the multivariate tunable dispersion of graphene. In this paper, we apply the GDM model to two emerging fields in the time-domain computational photonics.
In the first part, we further extend the GDM model to the Bi-Anisotropic (BA) case, where a full BA material tensor comes from homogenization procedure in the frequency domain. Conventional BA homogenization is a powerful multiscale technique for rapid prototyping and optimization of metasurfaces. With a new extension, the BA-GDM model characterizes artificial dispersion obtained from the mathematical equivalence of physical effects and enables the multiscale modeling of metasurfaces in the time domain.
Part 2 deals with new use of the GDM model in temperature-dependent time-domain simulations of phase change materials (PCMs). Optical PCMs, such as GST/GSST, are of critical utility in applications including, e.g., programmable metasurfaces, and nonvolatile memory. Typically, dispersions of amorphous and crystalline phases of PCMs are fitted separately in the frequency domain with a combination of the Tauc-Lorentz and Gauss terms, while Bruggeman’s mixing rule describes the transition states. Significantly advancing the-state-of-the-art, our GDM characterization describes dependency on temperature and crystallization levels explicitly and enables full wave modeling of PCMs in the time domain.
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 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.
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.
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