Optical phase change materials (O-PCMs), a unique group of materials featuring exceptional optical property contrast upon a solid-state phase transition, have found widespread adoption in photonic applications such as switches, routers and reconfigurable meta-optics. Current O-PCMs, such as Ge–Sb–Te (GST), exhibit large contrast of both refractive index (Δn) and optical loss (Δk), simultaneously. The coupling of both optical properties fundamentally limits the performance of many applications. Here we introduce a new class of O-PCMs based on Ge–Sb–Se–Te (GSST) which breaks this traditional coupling. The optimized alloy, Ge2Sb2Se4Te1, combines broadband transparency (1–18.5 μm), large optical contrast (Δn = 2.0), and significantly improved glass forming ability, enabling an entirely new range of infrared and thermal photonic devices. We further demonstrate nonvolatile integrated optical switches with record low loss and large contrast ratio and an electrically-addressed spatial light modulator pixel, thereby validating its promise as a material for scalable nonvolatile photonics.

Active metasurfaces promise reconfigurable optics with drastically improved compactness, ruggedness, manufacturability, and functionality compared to their traditional bulk counterparts. Optical phase change materials (O-PCMs) offer an appealing material solution for active metasurface devices with their large index contrast and nonvolatile switching characteristics. Here we report what we believe to be the first electrically reconfigurable nonvolatile metasurfaces based on O-PCMs. The O-PCM alloy used in the devices, Ge2Sb2Se4Te1 (GSST), uniquely combines giant non-volatile index modulation capability, broadband low optical loss, and a large reversible switching volume, enabling significantly enhanced light-matter interactions within the active O-PCM medium. Capitalizing on these favorable attributes, we demonstrated continuously tunable active metasurfaces with record half-octave spectral tuning range and large optical contrast of over 400%. We further prototyped a polarization-insensitive phase-gradient metasurface to realize dynamic optical beam steering.

Active metasurfaces, whose optical properties can be modulated post-fabrication, have emerged as an intensively explored field in recent years. 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 in 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 and propose a new figure-of-merit (FOM) tailored for reconfigurable meta-optics. We implement the approach to realize a high-performance varifocal metalens operating at 5.2 μm wavelength. The reconfigurable metalens features a record large switching contrast ratio of 29.5 dB. We further validate aberration-free and multi-depth imaging using the metalens, which represents a key experimental demonstration of a non-mechanical tunable metalens with diffraction-limited performance.

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A highly scalable approach for producing surface‐enhanced Raman spectroscopy substrates is introduced. The novel method involves assembling individual nanoparticles in pre‐defined templates, one particle per template, forming a high denisity of nanogaps over large areas, while decoupling nanostructure synthesis from placement.

Reconfigurable photonic systems featuring minimal power consumption are crucial for integrated optical devices in real‐world technology. Current active devices available in foundries, however, use volatile methods to modulate light, requiring a constant supply of power and significant form factors. Essential aspects to overcome these issues are the development of nonvolatile optical reconfiguration techniques which are compatible with on‐chip integration with different photonic platforms and do not disrupt their optical performances. Herein, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that uses undoped‐graphene microheaters to thermally and reversibly switch the optical phase‐change material Ge2Sb2Se4Te1 (GSST). An in situ Raman spectroscopy method is utilized to demonstrate, in real‐time, reversible switching between four different levels of crystallinity. Moreover, a 3D computational model is developed to precisely interpret the switching characteristics, and to quantify the impact of current saturation on power dissipation, thermal diffusion, and switching speed. This model is used to inform the design of nonvolatile active photonic devices; namely, broadband Si3N4 integrated photonic circuits with small form‐factor modulators and reconfigurable metasurfaces displaying 2π phase coverage through neural‐network‐designed GSST meta‐atoms. This framework will enable scalable, low‐loss nonvolatile applications across a diverse range of photonics platforms.

Metal-dielectric nanolaminates represent a class of hyperbolic metamaterials with uniaxial permittivity tensor. In this study, we critically compare permittivity extraction of nanolaminate samples using two techniques: polarized reflectometry vs. spectroscopic anisotropic ellipsometry. Both Au/MgF2 and Ag/MgF2 metal-dielectric stacks are examined. We demonstrate the applicability of the treatment of the multilayered material as a uniaxial medium and compare the derived optical parameters to those expected from the effective medium approximation. We also experimentally compare the effect of varying the material outer layer on the homogenization of the composite. Additionally, we introduce a simple empirical method of extracting the epsilon-near-zero point of the nanolaminates from normal incidence reflectance. The results of this study are useful in accurate determination of the hyperbolic material permittivity and in the ability to tune its optical properties.

We have established a method to quantify and optimize the plasmonic behavior of aluminum thin films by coupling spectroscopic ellipsometry into surface plasmon polaritons using a liquid prism cell in a modified Otto configuration. This procedure was applied to Al thin films deposited by four different methods, as well as to single crystal Al substrates, to determine the broadband optical constants and calculate plasmonic figures of merit. The best performance was achieved with Al films that have been sputter-deposited at high temperatures of 350°C, followed by chemical mechanical polishing. This combination of temperature and post-processing produced aluminum films with both large grain size and low surface roughness. Comparing these figures of merit with literature values of gold, silver, and copper shows that at blue and ultraviolet wavelengths, optimized aluminum has the highest figure of merit of all materials studied. We further employ the Ashcroft and Sturm theory of optical conductivity to extract the electron scattering times for the Drude and effective interband transitions, interband transition energies, and the optical mass of electrons.