Resonant cavity structures integrated with phase change material germanium antimony telluride (GST) function as angular insensitive mid-infrared optical filters. The one-dimensional (1D) sub-wavelength grating structures consisting of GST resonators embedded in metallic (Ag) film act as Fabry-Perot resonators with observable transmission resonances, that can be tuned by thermal excitation when GST switches from amorphous to crystalline state, while maintaining angular insensitivity up to 60 degrees. Modeling and experimental results of an interdigitated design of the 1D resonant structure for reconfigurable applications by electrical switching of the transmission spectra of the optical filter will be presented.
This letter presents a method for the release and sorting of gold nanoparticles (AuNP) from a soft substrate with an optothermal mechanical (OTM) method. The OTM method relies on the heating of AuNPs on a soft substrate via a continuous-wave laser. An AuNP absorbs the energy from the focused beam and transfers the heat to the substrate beneath it. The induced heat causes a rapid thermal expansion of the substrate, imparting an impulse to the AuNP and releasing it from the substrate. The release of an AuNP from a PMMA substrate of different thicknesses is studied. The release angle is determined by the polymer surface thickness, which affects the printing accuracy. Therefore, the release of an AuNP from a soft substrate of different thicknesses is investigated. The heat that can be generated within an AuNP depends on its size upon absorption. Generally, a smaller AuNP needs higher laser intensity to overcome the Van der Waal force to be released from the substrate. Therefore, the mixed sizes of AuNPs can be selected and sorted by their different release threshold. In this paper, the successful sorting of two types of AuNPs from a substrate to a receiver substrate in air condition is demonstrated. The OTM method paves a new way to separate and purify nanoparticles directly in a gaseous environment.
Spectroscopic measurements are used in increasingly diverse areas of manufacturing, disease detection, food quality inspection, indoor lighting control, etc. Commonly used spectral decomposition methods utilize several discrete dispersive optical elements to split the incoming light into its frequency components and direct them onto a linear photodetector array. In our previous work, we demonstrated that such mechanically fragile systems can be replaced by thin film dielectric Fourier spectral filters. However, the main disadvantage of this technique is the need for multiple filters with varying dielectric Fabry-Perot cavity lengths, which requires extensive fabrication processes to lithographically pattern and etch. In this work, we demonstrate a novel fabrication of a continuously variable filter, using glancing angle deposition, that can produce 10× more Fourier filters in a single deposition run without the need for lithographic patterning. We apply this method to a commercial off-the-shelf 38-channel linear photodetector array and demonstrate the ability to quickly decompose the incoming signal using only half of the available channels. This novel technique has the potential to enable highly compact and highly robust spectrometers that could be integrated into many handheld devices
: We present a unique route to realize a novel class of intrinsically chiral nano-helices that achieves the critical goal of demonstrating high-speed control of opto-chirality over 50,000 cycles via the optically active and tunable Ge2Sb2Te5 nanopatterned medium.
Chalcogenide phase change materials (PCMs) are uniquely suited for spectral tuning applications due to their contrasting dielectric material properties. Recent headway has been made towards realizing tunable photonic devices using twodimensional, sub-wavelength resonators by carefully designing geometries that optimize optical, electrical, and thermal performances using multi-physics analyses and machine learning. In this paper, we tackle two other essential aspects for creating application-specific, tunable PCM devices: (1) scalability of the device size and (2) high-throughput fabrication techniques. We employ a deep ultraviolet (DUV) stepper projection lithography to manufacture over 100 densely packed GST metasurfaces, each with a sample size of 5×7 mm2, all on a 4-inch Al2O3 wafer. These metasurface structures were discovered using artificial neural network (ANN) techniques and confirmed by finite-difference-time domain calculations. The primary structures under investigation were nanobar configurations enabling amplitude modulation at short-wave infrared wavelengths to realize efficient optical switches for free space optical multiplexing. The DUV fabrication technique can easily be extended to other metasurface geometries to demonstrate multi-functional, non-volatile photonic devices.
We present the design of a transmission filter in mid-infrared and its experimental verification using phase change material GST (Germanium Antimony Telluride). Progressively increasing the annealing temperature of GST controls the crystalline structure, allowing the refractive index to increase significantly in a steady rate. One-dimensional metal dielectric sub-wavelength grating device, such that the dielectric segments are proportioned to decouple any angular-dependent resonance. Incorporating GST between metal gratings allows transmission wavelengths to be actively tuned as annealing increases refractive index. Amorphous and crystalline GST devices show transmission resonances up to 60 degrees indicate that angular-independence is preserved during material excitation.
The purpose of the research is to study the novel structure metal-insulator-metal (MIM) rectified antenna (rectenna) and its efficiency for optical frequencies mixing and rectification. Semiconductor diodes have many imperfections such as heat problem and slow response, while MIM devices have less heat problem issues and have response times in the order of femtoseconds.
A magnetron co-sputtering system was used for producing nickel-doped Ge2Sb2Te5 (GST-Ni) thin films. The nickel content in the thin film was adjusted by the ratio of the plasma discharge power applied to the GST and nickel targets, as well as a physical shuttering technique to further control the nickel deposition rate. The doping concentration of the film was confirmed using Energy Dispersion Spectroscopy (EDS) technique. Results from a four-point probe measurement indicate that the nickel doping can reduce the resistivity of GST in the amorphous state by nearly three orders of magnitude. The dopant’s influence on crystallization behavior was studied by analyzing X-Ray Diffraction (XRD) patterns of the pure GST and GST-Ni at different annealing temperatures. To examine the structural changes due to the nickel dopant, the thin films were investigated with the aid of Raman scattering. Additionally, we extracted the optical constants for both the amorphous and crystalline states of undoped-GST and GST-Ni films by ellipsometry. The results indicate that at low doping concentrations nickel does not appreciably affect the optical constants, but dramatically improves the electrical conductivity. Therefore, nickel-doping of GST a viable method for designing optical devices for lower operating voltages at higher switching speeds.
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