University General - Research Publications
Permanent URI for this collection
Search Results
1 - 10 of 17
-
ItemMiniaturizing color-sensitive photodetectors via hybrid nanoantennas toward submicrometer dimensions(AMER ASSOC ADVANCEMENT SCIENCE, 2022-11-25)Digital camera sensors use color filters on photodiodes to achieve color selectivity. As the color filters and photosensitive silicon layers are separate elements, these sensors suffer from optical cross-talk, which sets limits to the minimum pixel size. Here, we report hybrid silicon-aluminum nanostructures in the extreme limit of zero distance between color filters and sensors. This design could essentially achieve submicrometer pixel dimensions and minimize the optical cross-talk arising from tilt illuminations. The designed hybrid silicon-aluminum nanostructure has dual functionalities. Crucially, it supports a hybrid Mie-plasmon resonance of magnetic dipole to achieve color-selective light absorption, generating electron hole pairs. Simultaneously, the silicon-aluminum interface forms a Schottky barrier for charge separation and photodetection. This design potentially replaces the traditional dye-based filters for camera sensors at ultrahigh pixel densities with advanced functionalities in sensing polarization and directionality, and UV selectivity via interband plasmons of silicon.
-
ItemHigh resolution multispectral spatial light modulators based on tunable Fabry-Perot nanocavities(SPRINGERNATURE, 2022-05-17)Spatial light modulators (SLMs) are the most relevant technology for dynamic wavefront manipulation. They find diverse applications ranging from novel displays to optical and quantum communications. Among commercial SLMs for phase modulation, Liquid Crystal on Silicon (LCoS) offers the smallest pixel size and, thus, the most precise phase mapping and largest field of view (FOV). Further pixel miniaturization, however, is not possible in these devices due to inter-pixel cross-talks, which follow from the high driving voltages needed to modulate the thick liquid crystal (LC) cells that are necessary for full phase control. Newly introduced metasurface-based SLMs provide means for pixel miniaturization by modulating the phase via resonance tuning. These devices, however, are intrinsically monochromatic, limiting their use in applications requiring multi-wavelength operation. Here, we introduce a novel design allowing small pixel and multi-spectral operation. Based on LC-tunable Fabry-Perot nanocavities engineered to support multiple resonances across the visible range (including red, green and blue wavelengths), our design provides continuous 2π phase modulation with high reflectance at each of the operating wavelengths. Experimentally, we realize a device with 96 pixels (~1 μm pitch) that can be individually addressed by electrical biases. Using it, we first demonstrate multi-spectral programmable beam steering with FOV~18° and absolute efficiencies exceeding 40%. Then, we reprogram the device to achieve multi-spectral lensing with tunable focal distance and efficiencies ~27%. Our design paves the way towards a new class of SLM for future applications in displays, optical computing and beyond.
-
ItemNo Preview AvailableA Novel Optical Assay System for Bilirubin Concentration Measurement in Whole Blood(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2022-02)As a biomarker for liver disease, bilirubin has been utilized in prognostic scoring systems for cirrhosis. While laboratory-based methods are used to determine bilirubin levels in clinical settings, they do not readily lend themselves to applications outside of hospitals. Consequently, bilirubin monitoring for cirrhotic patients is often performed only intermittently; thus, episodes requiring clinical interventions could be missed. This work investigates the feasibility of measuring bilirubin concentration in whole porcine blood samples using dual-wavelength transmission measurement. A compact and low-cost dual-wavelength transmission measurement setup is developed and optimized to measure whole blood bilirubin concentrations. Using small volumes of whole porcine blood (72 µL), we measured the bilirubin concentration within a range corresponding to healthy individuals and cirrhotic patients (1.2-30 mg/dL). We demonstrate that bilirubin levels can be estimated with a positive correlation (R-square > 0.95) and an accuracy of ±1.7 mg/dL, with higher reliability in cirrhotic bilirubin concentrations (> 4 mg/dL) - critical for high-risk patients. The optical and electronic components utilized are economical and can be readily integrated into a miniature, low-cost, and user-friendly system. This could provide a pathway for point-of-care monitoring of blood bilirubin outside of medical facilities (e.g., patient's home).
-
ItemMid-infrared Magnetic Mirror Based on a Hybrid Metal/Dielectric Metasurface(IEEE, 2018)We propose a hybrid metal/dielectric metasurface that functions as a mid-infrared magnetic mirror. It consists amorphous silicon cuboids on gold. The physical mechanism is explained by image theory. Measured reflection spectra agree with simulations.
-
ItemRoom temperature in-plane ferroelectricity in van der Waals In2Se3(AMER ASSOC ADVANCEMENT SCIENCE, 2018-07)Van der Waals (vdW) assembly of layered materials is a promising paradigm for creating electronic and optoelectronic devices with novel properties. Ferroelectricity in vdW layered materials could enable nonvolatile memory and low-power electronic and optoelectronic switches, but to date, few vdW ferroelectrics have been reported, and few in-plane vdW ferroelectrics are known. We report the discovery of in-plane ferroelectricity in a widely investigated vdW layered material, β'-In2Se3. The in-plane ferroelectricity is strongly tied to the formation of one-dimensional superstructures aligning along one of the threefold rotational symmetric directions of the hexagonal lattice in the c plane. Surprisingly, the superstructures and ferroelectricity are stable to 200°C in both bulk and thin exfoliated layers of In2Se3. Because of the in-plane nature of ferroelectricity, the domains exhibit a strong linear dichroism, enabling novel polarization-dependent optical properties.
-
ItemGeneralized Method of Images and Reflective Color Generation from Ultrathin Multipole Resonators(AMER CHEMICAL SOC, 2018-06-01)The multipole expansion has found limited applicability for optical dielectric resonators in inhomogeneous environment, such as on the surface of substrates. Here, we generalize the method of images to multipole analysis for light scattering by dielectric nanoparticles on conductive substrates. We present examples illustrating the physical insight provided by our method, including selection rules governing the excitation of the multipoles. We propose and experimentally demonstrate a new mechanism to generate high resolution surface color. The dielectric resonators employed are very thin (less than 50 nm), i.e., similar in thickness to the plasmonic resonators that are currently being investigated for structural color. The generalized method of images opens up new prospects for design and analysis of metasurfaces and optical dielectric resonators.
-
ItemControlling the Light Absorption in a Photodetector Via Nanowire Waveguide Resonances for Multispectral and Color Imaging(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2018-11-01)The responsivity spectrum of a photodetector is one of its key specifications. It ultimately originates from the combination of the absorption spectrum of the photosensitive region and the internal quantum efficiency. Many applications of photodetectors would benefit from an improved ability to tailor the responsivity spectrum. This is particularly true for color and multispectral imaging. The absorption spectrum of a bulk (unstructured) semiconductor is fixed however, being determined by its complex refractive index. Here, we review recent work that demonstrates that the absorption spectrum of a photodetector can be controlled via waveguide resonances in semiconductor nanowires. We discuss the physical interpretation for this phenomenon. We review work in which p-i-n photodiodes were incorporated into vertically oriented silicon nanowires, and then used for color imaging. We review work in which tandem-style photodetectors were demonstrated, with a p-i-n silicon nanowire photodiode formed above an n-i-p planar silicon photodiode. We review work in which narrowband photodetection across the visible-to-infrared was demonstrated using germanium nanowires. Finally, we describe related work in which silicon nanowires have been explored for other applications, namely solar cells.
-
ItemVertical Ge-Si Nanowires with Suspended Graphene Top Contacts as Dynamically Tunable Multispectral Photodetectors(AMER CHEMICAL SOC, 2019-03-20)Numerous applications would be enabled by pixels for multispectral imaging whose spectral responses can be dynamically tuned and that can be potentially manufactured at low cost. Here, we show such a capability, by experimentally demonstrating arrays of vertically oriented germanium–silicon heterojunction nanowires with graphene top contacts. Our devices present opportunities for multispectral imaging because their responsivity spectra can be tailored by choice of nanowire radius for enhanced absorption at certain wavelengths across the visible to short-wave infrared. Importantly, these responsivity spectra can also be dynamically tuned by bias voltage. We demonstrate this experimentally by tuning the responsivity peak of a single pixel across the visible region by varying the bias voltage and by showing that this would allow red/green/blue channels to be reconstructed. This opens the exciting prospect of a single pixel that can resolve color (i.e., replacing the three red/green/blue pixels of traditional approaches) or even resolve several bands for multispectral imaging.
-
Item
-
Item