Electrical and Electronic Engineering - Research Publications
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ItemNo Preview AvailableMid-infrared spectral reconstruction with dielectric metasurfaces and dictionary learning(Optica Publishing Group, 2022-05-15)Mid-infrared (MIR) spectroscopy has numerous industrial applications and is usually performed with Fourier-transform infrared (FTIR) spectrometers. While these work well for many purposes, there is currently much interest in alternative approaches that are smaller and lighter, i.e., MIR microspectrometers. Here we investigate all-dielectric metasurfaces as spectral filters for MIR microspectrometers. Two metasurface types are studied. For the first, we design, fabricate, and test a metasurface with a narrow and angularly tunable transmission stop band. We use it to reconstruct the transmission spectra of various materials. The second metasurface, investigated theoretically, possesses narrow passband features via symmetry-protected bound states in the continuum.
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ItemCompact Chemical Identifier Based on Plasmonic Metasurface Integrated with Microbolometer Array(WILEY-V C H VERLAG GMBH, 2022-04)Abstract The identification of chemicals from their mid‐infrared spectra has applications that include industrial production of chemicals, food production, pharmaceutical manufacturing, and environmental monitoring. This is generally done using laboratory benchtop tools, such as the Fourier transform infrared spectrometer. Although such systems offer high performance, alternative platforms offering reduced size, weight, and cost can enable a host of new applications, e.g. in consumer personal electronics. Here a compact microspectrometer platform for chemical identification, comprising a mid‐infrared metasurface integrated with a lightweight (≈1 g) and very small (≈1 cm3) microbolometer‐based thermal camera is experimentally demonstrated. A machine learning algorithm is trained to analyze the microspectrometer output and classify chemicals based on their mid‐infrared fingerprints. High accuracy identification of four liquid chemicals, concentration quantification of ethyl lactate in cyclohexane down to subpercentage levels, and the classification of food and drug samples is demonstrated.
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ItemNo Preview AvailableGenetic optimization of mid-infrared filters for a machine learning chemical classifier.(Optica Publishing Group, 2022-05-23)Miniaturized mid-infrared spectrometers present opportunities for applications that range from health monitoring to agriculture. One approach combines arrays of spectral filters with infrared photodetectors, called filter-array detector-array (FADA) microspectrometers. A paper recently reported a FADA microspectrometer in tandem with machine learning for chemical identification. In that work, a FADA microspectrometer with 20 filters was assembled and tested. The filters were band-pass, or band-stop designs that evenly spanned the microspectrometer's operating wavelength range. However, given that a machine learning classifier can be trained on an arbitrary filter basis, it is not apparent that evenly spaced filters are optimal. Here, through simulations with noise, we use a genetic algorithm to optimize six bandpass filters to best identify liquid and gaseous chemicals. We report that the classifiers trained with the optimized filter sets outperform those trained with evenly spaced filter sets and those handpicked to target the absorption bands of the chemicals investigated.
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ItemSpectrally Selective Mid-Wave Infrared Detection Using Fabry-Pérot Cavity Enhanced Black Phosphorus 2D Photodiodes.(American Chemical Society, 2020-10-27)Thin two-dimensional (2D) material absorbers have the potential to reduce volume-dependent thermal noise in infrared detectors. However, any reduction in noise must be balanced against lower absorption from the thin layer, which necessitates advanced optical architectures. Such architectures can be particularly effective for applications that require detection only within a specific narrow wavelength range. This study presents a Fabry-Pérot cavity enhanced bP/MoS2 midwave infrared (MWIR) photodiode. This simple structure enables tunable narrow-band (down to 0.42 μm full width at half-maximum) photodetection in the 2-4 μm range by adjusting the thickness of the Fabry-Pérot cavity resonator. This is achieved while maintaining room-temperature performance metrics comparable to previously reported 2D MWIR detectors. Zero bias specific detectivity and responsivity values of up to 1.7 × 109 cm Hz1/2 W-1 and 0.11 A W-1 at λ = 3.0 μm are measured with a response time of less than 3 ns. These results introduce a promising family of 2D detectors with applications in MWIR spectroscopy.
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ItemVisible to Short-Wave Infrared Photodetectors Based on ZrGeTe4 van der Waals Materials(AMER CHEMICAL SOC, 2021-09-29)The self-terminated, layered structure of van der Waals materials introduces fundamental advantages for infrared (IR) optoelectronic devices. These are mainly associated with the potential for low noise while maintaining high internal quantum efficiency when reducing IR absorber thicknesses. In this study, we introduce a new van der Waals material candidate, zirconium germanium telluride (ZrGeTe4), to a growing family of promising IR van der Waals materials. We find the bulk form ZrGeTe4 has an indirect band edge around ∼0.5 eV, in close agreement with previous theoretical predictions. This material is found to be stable up to 140 °C and shows minimal compositional variation even after >30 days storage in humid air. We demonstrate simple proof-of-concept broad spectrum photodetectors with responsivities above 0.1 AW-1 across both the visible and short-wave infrared wavelengths. This corresponds to a specific detectivity of ∼109 cm Hz1/2 W-1 at λ = 1.4 μm at room temperature. These devices show a linear photoresponse vs illumination intensity relationship over ∼4 orders of magnitude, and fast rise/fall times of ∼50 ns, also verified by a 3 dB roll-off frequency of 5.9 MHz. As the first demonstration of photodetection using ZrGeTe4, these characteristics measured on a simple proof-of-concept device show the exciting potential of the ZrGeTe4 for room temperature IR optoelectronic applications.
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ItemCopper Tetracyanoquinodimethane (CuTCNQ): A Metal-Organic Semiconductor for Room-Temperature Visible to Long-Wave Infrared Photodetection(AMER CHEMICAL SOC, 2021-08-18)Mid-wave and long-wave infrared (MWIR and LWIR) detection play vital roles in applications that include health care, remote sensing, and thermal imaging. However, detectors in this spectral range often require complex fabrication processes and/or cryogenic cooling and are typically expensive, which motivates the development of simple alternatives. Here, we demonstrate broadband (0.43-10 μm) room-temperature photodetection based on copper tetracyanoquinodimethane (CuTCNQ), a metal-organic semiconductor, synthesized via a facile wet-chemical reaction. The CuTCNQ crystals are simply drop-cast onto interdigitated electrode chips to realize photoconductors. The photoresponse is governed by a combination of interband (0.43-3.35 μm) and midgap (3.35-10 μm) transitions. The devices show response times (∼365 μs) that would be sufficient for many infrared applications (e.g., video rate imaging), with a frequency cutoff point of 1 kHz.
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ItemLong-Wave Infrared Photodetectors Based on 2D Platinum Diselenide atop Optical Cavity Substrates(AMER CHEMICAL SOC, 2021-04-27)Long-wave infrared (LWIR) photodetection is of high technological importance, having a wide range of applications that include thermal imaging and spectroscopy. Two-dimensional (2D) noble-transition-metal dichalcogenides, platinum diselenide (PtSe2) in particular, have recently shown great promise for infrared detection. However, previous studies have mainly focused on wavelengths up to the short-wave infrared region. In this work, we demonstrate LWIR photodetectors based on multilayer PtSe2. In addition, we present an optical cavity substrate that enhances the light-matter interaction in 2D materials and thus their photodetection performance in the LWIR spectral region. The PtSe2 photoconductors fabricated on the TiO2/Au optical cavity substrate exhibit responsivities up to 54 mA/W to LWIR illumination at a wavelength of 8.35 μm. Moreover, these devices show a fast photoresponse with a time constant of 54 ns to white light illumination. The findings of this study reveal the potential of multilayer PtSe2 for fast and broadband photodetection from visible to LWIR wavelengths.
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ItemAlgorithmic Spectral Reconstruction Using Angularly Tuned Zero-Contrast Gratings(IEEE, 2020)We experimentally demonstrate the algorithmic reconstruction of the infrared transmission spectrum of a polymer using a zero-contrast waveguide-grating metasurface as a filter. By changing the metasurface angle, a variety of filter functions are obtained.
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ItemGeometric Phase Metasurface Hologram for Optical Tractor Beam Generation(OSA & IEEE, 2020-01-01)We present a geometric phase silicon metasurface hologram design intended to produce a non-diffracting solenoid beam. Such optical beams have been shown to exert long range retrograde (i.e. toward source) optical forces on light-scattering particles.
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ItemLong -Wave In a ed Photodetectors Based on Platinum Diselenide(IEEE, 2020)We demonstrate long wave infrared photodetectors based on the transition metal dichalcogenide platinum diselenide (PtSe2) in its bulk form for the first time to our knowledge. Fabricated devices show sub-millisecond response times.