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.
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 mid-infrared (mid-IR) spectral region contains the characteristic vibrational absorption bands of most molecules as well as two atmospheric transmission windows, and is therefore of critical importance to many biomedical, military, and industrial applications such as spectroscopic sensing, thermal imaging, free-space communications, and infrared countermeasures. Metasurface devices operating in the mid-IR potentially offer significantly reduced size, weight, and cost compared to traditional bulk optics, but they are also challenged with unique material and processing requirements. By combining high-index, broadband transparent dielectric materials with a Huygens metasurface design, we have experimentally realized high-performance metasurface devices with a low-profile, deep sub-wavelength thickness. Based on the platform, we demonstrated single-layer metalenses with focusing efficiencies up to 75% and diffraction-limited performance over a record field of view close to 180 degrees. These meta-optical devices can provide significantly enhanced design flexibility for future infrared optical systems.
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