Metasurfaces offer flexibility for expanding functionality and reducing the size of optical systems by providing optical functionality from a flat surface. Previous work has demonstrated a rapid fabrication and testing process for wafers containing multiple 1-centimeter diameter metalenses that can be applied towards mass manufacturing. However, quality feedback was limited to analyzing imaging performance parameters such as the modulation transfer function and focal length. These techniques do not give direct feedback about specific manufacturing errors. Currently, getting this feedback still requires expensive, time-intensive processes such as scanning electron microscope (SEM) measurements or local area interferometry, which tend to have a small field of view. Theoretical investigation suggests that phase errors in the metasurface phase profile result in a shift in diffraction efficiency away from the first order and into the other diffraction orders, zero order, second, third, etc. We exploit this concept to comprehensively characterize metalens performance, including the analysis of standard image quality parameters and extending the study to multiple diffraction orders. An extensive set of measurements of the relative efficiency of the diffraction orders is presented for a set of fabricated metalenses alongside SEM measurements to cross-validate the presence of manufacturing defects. This will establish the extent to which current conventional CMOS processing and manufacturing techniques can be applied to metasurface optics by indicating uniformity and yield characteristics across positions and wafers.
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.
Optical metasurfaces are designed to control light similarly to conventional refractive optics, but with considerably less size and weight. They manipulate light based on the designed scattering from subwavelength resonant nanostructures within the surface. Such devices have only recently been fabricated. We characterized the performance of a 4-cm-focallength infrared dielectric metasurface lens using a scanning InSb detector array to record the intensity field behind the lens through its focal point and an optical scatterometer to measure its scatter. For the scatter measurements, a 5-mm-diameter beam illuminated a subsection of the metasurface at ten locations across the 40-mm extent of the lens to evaluate scattering in each subsection. The affected beam was steered through the lens’ focal point and expanded beyond it due to the 50-cm length of the scatterometer’s measurement arm. In general, the metasurface had scattering “shoulders” at angles outside the intended focal area about 2 orders of magnitude in transmission distribution space (Sr-1) higher than those of either a comparable infrared refractive optic or a flat polished silicon substrate; an additional forward-scattering lobe and a colinear peak caused by light travelling through the metasurface unaffected, which are not typically observed in a refractive lens, were also observed.
Point defects in semiconductors are useful as quantum sensors, quantum emitters, and qubits for quantum computation. We have used ab initio quantum chemistry (supercell) calculations to model the photoluminescence of a new vanadium-nitrogen defect in diamond. Using ion implantation, we have attempted to synthesize this defect, and I will present spectroscopic analysis of our sample. Nanoscale positioning of defects is desired to improve the reliable coupling of defect centers to quantum photonic devices. I will discuss the merits of several methods for achieving this: introduction of functionalized seed molecules during diamond synthesis, laser annealing, and ion implantation. I will also present a scalable opto-thermal-mechanical printing method for additively releasing nanoparticles from a donor substrate and transferring them to a target substrate, such as a photonic device. Such integration is a crucial step towards realizing commercially scalable quantum sensing devices.
Acoustic wavelengths are about 5 orders of magnitude shorter than EM waves of the same frequency. This can be a critical advantage in the quest to further miniaturize devices that have dimensions linked to their characteristic resonance frequencies. Therefore, many novel multiferroic (MF) devices rely on the transduction of signals from EM radiation to surface and bulk acoustic waves, and yet acoustic wave interactions in complex MF heterostructures are poorly understood. Here, an all-optical interferometric imaging system is developed for two-dimensional scanning imaging of acoustic wave amplitudes with sub-angstrom surface displacement sensitivity and submicron spatial resolution. Measurement capability has been verified with a 50-MHz piezoelectric SAW bandpass filter, with the frequency spectrum showing similar behavior to the S21 transmission measured with a network analyzer, and with a linear dependence on the input power. Spatial dependence of the acoustic waves also behaves as expected, with the largest amplitude near the input electrode. Next, the system has been demonstrated to detect acoustic waves in MF heterostructure-based MEMS devices with frequencies up to 3 GHz. These detections pave the way for fast and reliable troubleshooting of new device designs involving acoustic waves, in which it may not be immediately clear to where or by what mechanism power is being dissipated.
Pixelated wiregrids are of great interest in polarimetric imagers, but there are no straightforward methods available for combining the uniform exposures of laser interference with a masking system to achieve pixels at different rotational angles. In this work we demonstrate a 266nm deep-UV interference lithography combined with a traditional i-line contact lithography to create such pixels. Aluminum wiregrids are first made, following by etching to create the pixels, and then a planarizing molybdenum film is used before patterning subsequent pixel arrays. The etch contrast between the molybdenum and the aluminum enables the release of the planarizing layer.
Ultrathin silver films (thickness below 10 nm) are of great interest as optical coatings on windows and plasmonic
devices. However, producing these films has been a continuing challenge because of their tendency to form clusters or
islands rather than smooth contiguous thin films. In this work we have studied the effect of Cu, Ge and ZnS as wetting
layers (1.0 nm) to achieve ultrasmooth thin silver films. The silver films (5 nm) were grown by RF sputter deposition on
silicon and glass substrates using a few monolayers of the different wetting materials. SEM imaging was used to
characterize the surface properties such as island formation and roughness. Also the optical properties were measured to
identify the optical impact of the different wetting layers. Finally, a multi-layer silver based structure is designed and
fabricated, and its performance is evaluated. The comparison between the samples with different wetting layers show
that the designs with wetting layers which have similar optical properties to silver produce the best overall performance.
In the absence of a wetting layer, the measured optical spectra show a significant departure from the model predictions,
which we attribute primarily to the formation of clusters.
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