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Featured Application: A configurable readout circuit for the focal plane array is designed that transmits information in the form of spike-encoding and supports different encoding methods. Spiking neural networks with different structures can be matched according to the task. Spiking neural networks inspired by biological models are gaining popularity in artificial intelligence due to their ability to solve diverse problems while reducing energy consumption. As a result of the trade-off between the need to transmit large amounts of data and the power consumption of hardware deployment, artificial vision systems are particularly well-suited to construction using spiking neural networks (SNNs). How to communicate with the neuromorphic network effectively is one of the challenges associated with building systems that utilize SNN systems. It is necessary to convert the data to spike form before they can be processed by an SNN as input, unless neuromorphic or event-triggered sensing systems are employed. We present a configurable circuit based on a focal plane array (FPA) capable of providing spike-encoded readout data at the pixel level. With this type of circuit, the current signal of the photoelectric sensor can be encoded into two spike encodings with different precision, which are sent for processing to SNNs. This provides image information at two different scales for the artificial vision system based on SNNs. With this feature, we can use this circuit and different SNN structures to build an artificial target recognition system that is closer to the biological visual system. [ABSTRACT FROM AUTHOR]

In this paper, the existing methodology for deselection of overly noisy elements within channels of an infrared (IR) focal plane array (FPA) with time delay integration (TDI) mode, designed to increase the signal-to-noise ratio (SNR) in the channels of a photodetector, is considered. As a result of the analysis, a disadvantage of the methodology was revealed, it is applicable only for IR FPA with 6 × 576 elements. To eliminate this disadvantage, a modification of the methodology for deselection of overly noisy elements was performed. The modification made it available to use the methodology for deselection within channels of an IR FPA with the TDI mode of any format. The modified methodology will be helpful to increase the SNR in the channels of the IR FPA regardless of the photodetector format. [ABSTRACT FROM AUTHOR]

Active millimeter-wave beamforming arrays and focal plane array antennas require extensive calibration to compensate for impairments, such as phase and gain variations between elements, as well as unintended coupling between changes in gain and phase. When far-field calibration methods are used for calibrating focal plane array antennas, the required size of the anechoic chamber is exceedingly large. For this reason, a near-field calibration method for millimeter-wave analog beamforming array antennas and focal plane array antennas is proposed. Nonidealities of the beamformer integrated circuits with vector modulators are taken into consideration, and a way to reduce the measurement set for vector modulators with high resolution is proposed. This method is both practical and achieves a good calibration as evidenced by measurements of the radiation patterns, and it is suitable for use in an automated factory calibration setup. The important trade-off between the radiated power and side-lobe level is highlighted.

Ongoing technological advances in photodetector material growth and processing, readout integrated circuits, and robust hybridization (packaging) methods for assembling high-resolution and small-pitch size pixel arrays are the main enabling factors for pushing the frontiers of high-performance Focal Plane Array (FPA) technologies for imaging systems. This paper details the development of analytical and numerical models and demonstrates their use to generate insights into the feasibility of two flip-chip assembly processes for packaging infrared (IR) detector chips. The modeling studies focus on the challenges of forming the indium interconnection arrays in the case of the FPA technologies using Group III-V compound semiconductor materials and ultra-fine pitch pixel array layouts. The accurate alignment of the IR detector chip onto the readout chip in the case of high-density pixel architectures is a critical requirement for the packaging process. To gain a better understanding of this requirement, which has a clear implication for the quality and subsequent reliability performance of the FPA, compression, and reflow bonding process models are developed using suitable modeling approaches and methods and then demonstrated for two distinctive focal plane array design configurations. The novelty of this work is in the developed modeling capabilities utilizing different computational methods, from large deformation and contact analysis finite element to energy-based and harmonic motion mechanics, to characterize and optimize the mechanical and dynamic non-linear behavior of the indium solder joints and their formation during FPA packaging. The feasibility of bonding techniques for different resolution FPAs and under flip-chip misalignment conditions is assessed. The modeling results pointed to a very strict, sub-micrometer flip-chip placement accuracy requirement for the assembly of FPAs with ultra-fine indium bump array resolution.

The relatively high atmospheric propagation of millimeter-waves (MMW) was found to be one of the most critical reasons for the development of reliable sensors for MMW detection. According to previous research works, it has been already shown that incident MMW radiation on a glow discharge detector (GDD) can increase the discharge current. Hence, the electrical mode of detection can be employed to detect the presence of MMW radiation. In this article, a new design of a row detector using GDDs as pixel elements, and the influence of MMW incidence on GDD's discharge current, were acquired using an elementary data acquisition (DAQ) platform. The DAQ system computes the averaged Fast Fourier Transform (FFT) spectrum of the time signal and returns the FFT results as magnitude based on the level of detection. An FFT-based signal acquisition proved to be a better alternative to the lock-in detection that was commonly used in MMW detection systems. This improved detection circuit provides enhanced noise filtering, thereby resulting in better MMW images within a short time. The overhead expense of the entire system is very low, as it can avoid lock-in amplifier stages that were previously used for signal enhancement. A scanning mechanism using a motorized translation stage (step motor) is involved to place and align the row detector in the image plane. The scanning can be carried out vertically to perform the imaging, by configuring the step motor after selecting the desired step size and position. A simplified version of the MMW detection circuit with a dedicated over-voltage protection facility is presented here. This made the detection system more stable and reliable during its operation. The MMW detection circuit demonstrated in this work was found to be a milestone to develop larger focal plane arrays (FPA) with very inexpensive sensor elements. [ABSTRACT FROM AUTHOR]

In the last decade, infrared imaging detectors trend has gone for smaller pixels and larger formats. Most of the time, this scaling is carried out at a given total sensitive area for a single focal plane array. As an example, QVGA 30 µm pitch and VGA 15 µm pitch exhibit exactly the same sensitive area. SXGA 10 µm pitch tends to be very similar, as well. This increase in format is beneficial to image resolution. However, this scaling to even smaller pixels raises questions because the pixel size becomes similar to the IR wavelength, but also to the typical transport dimensions in the absorbing material. Hence, maintaining resolution for such small pixel pitches requires a good control of the modulation transfer function and quantum efficiency of the array, while reducing the pixel size. This might not be obtained just by scaling the pixel dimensions. As an example, bulk planar structures suffer from excessive lateral diffusion length inducing pixel-to-pixel cross talk and thus degrading the modulation transfer function. Transport anisotropy in some type II superlattice structures might also be an issue for the diffusion modulation transfer function. On the other side, mesa structures might minimize cross talk by physically separating pixels, but also tend to degrade the quantum efficiency due to a non-negligible pixel fill factor shrinking down the pixel size. This paper discusses those issues, taking into account different material systems and structures, in the perspective of the expected future pixel pitch infrared focal plane arrays. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dark background is corrected for fine-scale fluctuations and large-scale trend changes. • The theoretical limit of dark background correction is defined for evaluating effect. • Spectral imaging effect with three different correction methods is compared. Dark currents in HgCdTe devices are the main factor that limit detector performance in infrared imaging systems, which may result in a reduced dynamic range and poor signal-to-noise ratio (SNR). In this paper, the theoretical limit of dark background correction is defined, and the correction effects of different methods are quantitatively evaluated. Based on accurate measurements of the focal plane array (FPA) temperature, the relationship between the FPA temperature and dark background is evaluated. The fluctuations are highly consistent; thus, the FPA temperature can be used to estimate the dark background of different pixels in real time. Moreover, the temperature of the opto-mechanical components is stabilized at 120 K to suppress instrument radiation, and the temperature of the electrical box is applied to correct gradient changes in the dark background at large time scales. As a result, the dark backgrounds of different pixels can be accurately corrected in real time. [ABSTRACT FROM AUTHOR]

In the last half-decade, the extended shortwave infrared (eSWIR) atmospheric band has become a focus of investigation for its potential to provide better object discrimination at range than the visible, as well as the near, shortwave, midwave, and longwave infrared bands, particularly in degraded visual environments such as smoke, dust, and smog. However, any detection band is only as useful as the best available detector, and thus, an investigation into the design of detectors for use in the eSWIR band is necessary before standards are established and applications put into practice. We examine the relationship between detector parameters and targeting performance in the eSWIR band for both passive and active detection. The effects of pixel pitch, dark current, read noise, frame rate, quantum efficiency, and well depth are examined and ranked in importance to an eSWIR system's performance. [ABSTRACT FROM AUTHOR]

Spiking neural networks inspired by biological models are gaining popularity in artificial intelligence due to their ability to solve diverse problems while reducing energy consumption. As a result of the trade-off between the need to transmit large amounts of data and the power consumption of hardware deployment, artificial vision systems are particularly well-suited to construction using spiking neural networks (SNNs). How to communicate with the neuromorphic network effectively is one of the challenges associated with building systems that utilize SNN systems. It is necessary to convert the data to spike form before they can be processed by an SNN as input, unless neuromorphic or event-triggered sensing systems are employed. We present a configurable circuit based on a focal plane array (FPA) capable of providing spike-encoded readout data at the pixel level. With this type of circuit, the current signal of the photoelectric sensor can be encoded into two spike encodings with different precision, which are sent for processing to SNNs. This provides image information at two different scales for the artificial vision system based on SNNs. With this feature, we can use this circuit and different SNN structures to build an artificial target recognition system that is closer to the biological visual system.

As we look forward to the next generation of hyperspectral infrared (IR) atmospheric sounders, grating spectrometers hold promise for improved performance (e.g., horizontal and spectral resolutions) and more rapid revisit while reducing the size and complexity of the instrument. We briefly revisit the technology used in the Atmospheric Infrared Sounder (AIRS), recognizing that it was developed in the 1990’s and has matured key technologies in the areas of IR detectors, optical coatings, gratings, and cryocoolers. AIRS has been an unqualified success not only as a science and operational mission but also as a technology demonstration of the reliability and simplicity of grating spectrometer IR sounding instruments. Advancements in focal plane arrays (FPAs) have enabled a new class of grating spectrometer IR sounders that offer more spectral channels on a single FPA, mitigating some of the issues seen in AIRS that used linear arrays. These improvements have been manifested in the CubeSat Infrared Atmospheric Sounder (CIRAS) brassboard instrument, developed at the California Institute of Technology Jet Propulsion Laboratory with industry partner Ball Aerospace. Further enhancements beyond those used in CIRAS enable the development of a new class of instruments with a very long-wavelength infrared response and a very high spatial resolution (

A new antenna system concept is presented where a wide-scan focal plane array antenna is used to achieve point-to-multipoint communication. The focal plane of a parabolic toroid reflector is populated with several antenna arrays, the positions of which determine the directions of the beams. This concept is investigated for beams pointed towards 0° (broadside) and 28° in azimuth. Each array allows for scanning an additional ±1° in azimuth and elevation. This allows for compensation of twist and sway of the antenna mast. Several array configurations are compared in terms of directivity and scan loss for such a system at E-band. It is found that an 8-by-8 array with an inter-element spacing of $0.7 \lambda _{0}$ results in an optimal directivity with a scan loss lower than 1dB when scanning ±1° in azimuth and elevation. For the 0° beam direction the directivity is 45.5dBi and for the 28° beam direction the directivity is 44.4dBi, showing the wide angle scanning properties of this system. An experimental system is built at K-band and measurements are performed showing this system in action. In the measurements an array of 8-by-8 is used with an inter-element spacing of $0.5 \lambda _{0}$ . The scan loss when scanning ±2° in azimuth and elevation is below 1dB. The directivity is 37.0dBi and 35.4dBi for the 0° and 28° beam directions, respectively. The spillover losses and aperture efficiencies are also found, as well as a relative metric for the transmitted power and the effective isotropic radiated power for both the E-band and K-band systems.

In comparison with traditional space infrared spectroscopy technology, the interference signals of a large focal plane array (FPA) can be used to obtain spectra over a larger area range and rapidly achieve large-scale coverage of hyperspectral remote sensing. However, the low signal-to-noise ratio of the interference signals limits the application of spectral data, especially when atmospheric detection occurs in the long-wavelength infrared (LWIR) band. In this paper, we construct an LWIR hyperspectral system of a Fourier transform spectrometer composed of a HgCdTe photovoltaic IR FPA and a Michelson interferometer. The LWIR interference signals are obtained by a high-frequency oversampling technique. We use the Kalman filter (KF) and its improved weighted adaptive Kalman filter (WAKF) to reduce the noise of multiple measured data of each pixel. The effect of overshoot and ringing artifacts on the objective signals is reduced by the WAKF. The applicability is studied by the interference signals from the different sampling frequencies and different pixels. The effectiveness is also verified by comparing the spectra of denoised interferograms with the reference spectrum. The experimental results show that the WAKF algorithm has excellent noise suppression, and the standard deviation of the interferogram can be reduced by 39.50% compared with that of KF. The WAKF is more advantageous in improving the signal-to-noise ratio of the interferogram and spectra. The results indicate that our system can be applied to atmospheric vertical detection and hyperspectral remote sensing over large area ranges because our denoised technique is suitable for large LWIR FPA. [ABSTRACT FROM AUTHOR]

Silicon-based complementary metal oxide semiconductors have revolutionized the field of imaging, especially infrared imaging. Infrared focal plane array imagers are widely applied to night vision, haze imaging, food selection, semiconductor detection, and atmospheric pollutant detection. Over the past several decades, the CMOS integrated circuits modified by traditional bulk semiconductor materials as sensitivity sensors for optoelectronic imagers have been used for infrared imaging. However, traditional bulk semiconductor material-based infrared imagers are synthesized by complicated molecular beam epitaxy, and they are generally coupled with expensive flip-chip-integrated circuits. Hence, high costs and complicated fabrication processes limit the development and popularization of infrared imagers. Emerging materials, such as inorganic–organic metal halide perovskites, organic polymers, and colloidal quantum dots, have become the current focus point for preparing CMOS-compatible optoelectronic imagers, as they can effectively decrease costs. However, these emerging materials also have some problems in coupling with readout integrated circuits and uniformity, which can influence the quality of imagers. The method regarding coupling processes may become a key point for future research directions. In the current review, recent research progress on emerging materials for infrared imagers is summarized. [ABSTRACT FROM AUTHOR]

Short wave infrared (SWIR) imaging has been used in various applications such as electronic board inspection, surveillance and gas detection. Unlike the conventional compound semiconductor focal plane array (FPA), in this work group IV back-illuminated imaging array with 320 $\times256$ pixels was demonstrated. For reference device with a diameter of 30 $\mu \text{m}$ , the dark current was 9.7 nA at 0 V. At 1550 nm, a responsivity of 0.61 A/W was obtained at −1 V using a Ge photodetector with a diameter of 75 $\mu \text{m}$. The image of a halogen lamp was successfully captured at room temperature with a pixel operating bias of 0 V. Showing great compatibility with the existing CMOS technology, group IV imaging array becomes one of the promising candidates to be applied in SWIR imaging area. [ABSTRACT FROM AUTHOR]

High-performance InAs/GaSb type-II superlattice infrared detectors and focal plane arrays (FPAs) are normally grown by molecular beam epitaxy (MBE). In this work, we demonstrate the first long-wavelength infrared InAs/GaSb superlattice FPA grown by metalorganic chemical vapor deposition (MOCVD) with clear image. High-quality superlattice material was obtained evidenced by sharp X-ray diffraction peaks and atomic flat surface. Electrical and optical measurements performed on single element detectors showed a 50% cut-off wavelength of $\sim 10.1~\mu \text{m}$ , a dark current density of $2.5\times 10^{-5}$ A/cm2, a peak responsivity of 0.88 A/W and a peak detectivity of $1.7\times 10^{11}$ cm $\cdot $ Hz1/2/W at 80 K. A $320\times256$ FPA with $30~\mu \text{m}$ pixel pitch was then fabricated. With an integration time of 1.9 ms and an applied bias of -0.1 V, the FPA shows an average operability of 96.96%, a non-uniformity of 4.97%, a noise equivalent temperature difference of 51.1 mK and a peak detectivity of $2.3\times 10^{10}$ cm $\cdot $ Hz1/2/W at 80 K without thinning down the substrate.

BackgroundSlow-degrading, fossil fuel-derived plastics can have deleterious effects on the environment, especially marine ecosystems. The production of bio-based, biodegradable plastics from or in plants can assist in supplanting those manufactured using fossil fuels. Polyhydroxybutyrate (PHB) is one such biodegradable polyester that has been evaluated as a possible candidate for relinquishing the use of environmentally harmful plastics.ResultsPHB, possessing similar properties to polyesters produced from non-renewable sources, has been previously engineered in sugarcane, thereby creating a high-value co-product in addition to the high biomass yield. This manuscript illustrates the coupling of a Fourier-transform infrared microspectrometer, equipped with a focal plane array (FPA) detector, with multivariate imaging to successfully identify and localize PHB aggregates. Principal component analysis imaging facilitated the mining of the abundant quantity of spectral data acquired using the FPA for distinct PHB vibrational modes. PHB was measured in the chloroplasts of mesophyll and bundle sheath cells, acquiescent with previously evaluated plant samples.ConclusionThis study demonstrates the power of IR microspectroscopy to rapidly image plant sections to provide a snapshot of the chemical composition of the cell. While PHB was localized in sugarcane, this method is readily transferable to other value-added co-products in different plants.

Nanocrystals (NCs) have reached a high level of maturity, enabling their integration into optoelectronic devices. The next challenge is the combination of several types of devices into one complex system to achieve better on‐chip integration. Here, an all‐HgTe‐NC active imaging setup operating in the short‐wave infrared (IR) is focused on. First, the design of an optimized IR light‐emitting diode (LED) is focused on. It is shown that a halide technology processing enables an increase of the electroluminescence signal by a factor of 3, while preserving a low turn‐on voltage and a high brightness (3 W sr−1 m−2). Then the degradation mechanism of this LED under continuous operation is unveiled and a shift from band edge to trap emission is shown. This degradation process can be strongly reduced thanks to the encapsulation and the thermal control of the LED. Lastly, the IR emission of the LED is imaged using a focal plane array whose active layer is also made of HgTe NCs, paving the way for all‐NC‐based active imaging setups. [ABSTRACT FROM AUTHOR]

A $15~\mu \text{m}$ pitch extended wavelength In0.83Ga0.17As/ InP mega-pixel focal plane array (FPA) with a format of 1280 $\times 1024$ and a spectral response range of 1150–2450 nm has been demonstrated for the first time. High fill factor up to >86%, low dark current densities down to < 133 nA/cm2, high quantum efficiencies up to >69%, were achieved by implementing novel high density micro-mesa array processing technologies. A proprietary wafer bowing control technique was developed, attaining a high pixel operability of 99.37%. Laboratory imaging was also demonstrated, showing potentiality for high resolution imaging applications in a wider SWIR spectrum range. [ABSTRACT FROM AUTHOR]

For the first time, the characteristics of an evolving commercial camera technology that can operate at millimeter-wave frequencies has been independently investigated. In this work, we benchmark the TeraSense camera against a custom-built single-pixel camera at W-band, for image quality and aperture reflectance. It is found that the Tera-1024 TeraSense camera exhibits limited image resolution and fidelity, with significant levels of systematic spatial noise. In a poor signal-to-noise ratio scenario, the addition of random noise exacerbates these problems. Possible causes of both beam and image distortion have been identified in quasi-optical applications, which gives important insight into the best use of (sub-)THz cameras and interpretation of their images. Inherent standing waves caused by the significant power reflectance of the camera aperture is investigated in detail. A simple W-band one-port quasi-optical scalar network analyzer is developed, to determine the levels of reflectance for both cameras, with its bespoke calibration routine derived from first principles - providing a low-cost solution for many non-destructive testing applications. It is found that the TeraSense camera (with additional RAM) and single-pixel camera (having default RAM) have measured reflectance values of 27% and 3%, respectively, over a corresponding aperture area ratio of approximately 714:1. While our single-pixel camera provides excellent image resolution and fidelity, it inherently suffers from very slow raster-scanning speeds and operational bandwidth limitations. For this reason, the TeraSense camera technology is excellent for performing qualitative measurements in real time, with the caveats outlined in this paper.

The relatively high atmospheric propagation of millimeter-waves (MMW) was found to be one of the most critical reasons for the development of reliable sensors for MMW detection. According to previous research works, it has been already shown that incident MMW radiation on a glow discharge detector (GDD) can increase the discharge current. Hence, the electrical mode of detection can be employed to detect the presence of MMW radiation. In this article, a new design of a row detector using GDDs as pixel elements, and the influence of MMW incidence on GDD’s discharge current, were acquired using an elementary data acquisition (DAQ) platform. The DAQ system computes the averaged Fast Fourier Transform (FFT) spectrum of the time signal and returns the FFT results as magnitude based on the level of detection. An FFT-based signal acquisition proved to be a better alternative to the lock-in detection that was commonly used in MMW detection systems. This improved detection circuit provides enhanced noise filtering, thereby resulting in better MMW images within a short time. The overhead expense of the entire system is very low, as it can avoid lock-in amplifier stages that were previously used for signal enhancement. A scanning mechanism using a motorized translation stage (step motor) is involved to place and align the row detector in the image plane. The scanning can be carried out vertically to perform the imaging, by configuring the step motor after selecting the desired step size and position. A simplified version of the MMW detection circuit with a dedicated over-voltage protection facility is presented here. This made the detection system more stable and reliable during its operation. The MMW detection circuit demonstrated in this work was found to be a milestone to develop larger focal plane arrays (FPA) with very inexpensive sensor elements.

Featured Application: An elementary method for MMW detection by GDD-LTF combination as single pixel for focal plane arrays. Performance enhancement of a very inexpensive millimeter-wave (MMW)/terahertz (THz) sensor for MMW/THz imaging systems is experimentally demonstrated in this study. The MMW sensor is composed of a glow discharge detector (GDD) and a light-to-frequency (LTF) converter combination. The experimental results given in this study show an improvement in the performance parameters of the detector element, such as the minimum detectable signal, as well as the signal to noise ratio (SNR) and the noise equivalent power (NEP), when a NIR long-pass filter was inserted between the GDD and the LTF combination. A detailed derivation of the NEP of this unique sensor is presented in this work. Based on this derivation and the experimental measurements, the NEP value was calculated. [ABSTRACT FROM AUTHOR]

We analyze the current state of research in the field of creating unipolar semiconductor barrier structures based on various materials for infrared photodetector arrays, which make it possible to reduce the dark currents and thereby improve the threshold characteristics and ensure operation at high cooling temperatures. The main ways of minimizing a barrier for holes in the valence band are considered by the example of a photosensitive structure based on the n-CMT layer. It is shown that the nBn barrier structures are an alternative for creating photodiode sensing matrices for the mid- and far-infrared photodetector arrays. [ABSTRACT FROM AUTHOR]

In comparison with traditional space infrared spectroscopy technology, the interference signals of a large focal plane array (FPA) can be used to obtain spectra over a larger area range and rapidly achieve large-scale coverage of hyperspectral remote sensing. However, the low signal-to-noise ratio of the interference signals limits the application of spectral data, especially when atmospheric detection occurs in the long-wavelength infrared (LWIR) band. In this paper, we construct an LWIR hyperspectral system of a Fourier transform spectrometer composed of a HgCdTe photovoltaic IR FPA and a Michelson interferometer. The LWIR interference signals are obtained by a high-frequency oversampling technique. We use the Kalman filter (KF) and its improved weighted adaptive Kalman filter (WAKF) to reduce the noise of multiple measured data of each pixel. The effect of overshoot and ringing artifacts on the objective signals is reduced by the WAKF. The applicability is studied by the interference signals from the different sampling frequencies and different pixels. The effectiveness is also verified by comparing the spectra of denoised interferograms with the reference spectrum. The experimental results show that the WAKF algorithm has excellent noise suppression, and the standard deviation of the interferogram can be reduced by 39.50% compared with that of KF. The WAKF is more advantageous in improving the signal-to-noise ratio of the interferogram and spectra. The results indicate that our system can be applied to atmospheric vertical detection and hyperspectral remote sensing over large area ranges because our denoised technique is suitable for large LWIR FPA.

• Mid-wavelength infrared photodetectors based on type II InAs/GaSb superlattice structures grown on InP substrate. • Suppression of propagation of threading dislocations because of thick GaSb buffer layer and two step growth of it. • Successful fabrication of 640 × 512 format 2D arrays with 15 μm-pixel pitch. • Clear Human face image with high operability under cooled operation. We report the growth and characterization of band gap engineered mid-wavelength infrared photodiode, pBiBn, based on type-II InAs/GaSb superlattices on InP substrate. InP substrates are attractive material because they have high transmittance in the mid-wavelength infrared region and near thermal expansion coefficient to Si read-out IC (ROIC). Misfit dislocations due to lattice mismatch between GaSb and InP were successfully suppressed by thick GaSb buffer layer and two step growth of it. The photoluminescence (PL) spectrum from the absorption layers exhibits a peak wavelength of 5.01 μm at 77 K. The distinct PL peak was observed even at 120 K, indicating the excellent crystalline quality of T2SLs grown on an InP substrate. The dark current densities of 292 × 10−6 A/cm2 at 77 K and cut off wavelength of 5.15 μm at 80 K were measured, respectively. A clear image was obtained by fabricated focal plane array of 640 × 512 pixels with 15 μm pixel pitch, and NEDT and defective pixel rate was 50 mK and less than 1 % at 100 K, respectively. [ABSTRACT FROM AUTHOR]

The photoelectric interconnection of matrix photodetectors in the medium-wave IR range of 320 × 256 elements with a step of 30 μm and 640 × 512 elements with a step of 15 μm based on indium antimonide is investigated. The dependence of the crosstalk value on the thickness of a thinned InSb bulk structure was determined. The interrelation of the elements of matrix photodetectors based on epitaxial indium antimonide is significantly less than the interrelation based on bulk indium antimonide. [ABSTRACT FROM AUTHOR]

HgCdTe is one of the most important materials for the fabrication of infrared detectors and focal plane arrays (FPAs) deployed in environments where high-energy particles, such as protons and neutrons, are present. We designed and fabricated HgCdTe-based FPAs that can be used in high neutron radiation environments and we measured their characteristics. The influence of the radiation on the infrared FPAs and cameras is investigated. HgCdTe material and devices are capable of maintaining high performances in a high energy neutron irradiation environment. For MWIR FPA directly facing a 2.59 × 108 n/cm2 s neutron flux beam (with the highest energy 66 MeV) for 1 h, the noise equivalent differential temperature (NEDT) increased ∼ 8 times after irradiation. However, NEDT decreased to 33 mK (compared to the original value of 21 mK) after one warming-up (to room temperature) and cooling-down cycle. The NEDT for the MWIR FPAs mounted parallel to the beam did not degrade (16 mK and 28 mK before irradiation, changed to 18 mK and 26 mK after irradiation, respectively). [ABSTRACT FROM AUTHOR]

Noise equivalent temperature difference (NETD) is an important figure of merit for infrared detectors. Lower NETD means that the detector can realize smaller temperature resolution and longer range recognition. In this work, we investigate the device performance, especially the NETD characteristics of a long-wavelength infrared (LWIR) photodetector based on InAs/GaSb type-II superlattice (T2SL). To achieve mK-level temperature-sensitivity, the effect of detector's intrinsic and extrinsic factors on NETD performance has been discussed. Through a series of efforts, a NETD value of 7 mK was realized for a T2SL detector with a 100% cutoff wavelength of 11.4 μm at 77 K. [ABSTRACT FROM AUTHOR]

InAs/GaAsSb type-II superlattice (T2SL) materials grown at a higher temperature and lattice-matched to InAs substrates are considered to have significant advantages in long wavelength infrared (LWIR) detection. In this work, an InAs/GaAsSb T2SL LWIR focal plane array (FPA) was fabricated and evaluated. The FPA has a format of $320\times256$ with a pixel pitch of 30 $\mu \text{m}$ and exhibits a 100% cutoff wavelength of 9.5 $\mu \text{m}$ at 80 K. Under a bias of -0.02V, the detectors show a dark current of $1.7\times 10^{-5}$ A/cm2 and a differential resistance-area of $1.5\times 10^{3} \Omega \cdot \text {cm}^{2}$. The noise equivalent temperature difference and operability of the FPA are 20.7 mK and 99.2% respectively under an integration time of $400~\mu \text{s}$ , a 300 K background and F/2.0 optics. This high-performance FPA further verifies the feasibility of InAs/GaAsSb T2SL in LWIR detection. [ABSTRACT FROM AUTHOR]

This article presents a compact W‐band quasi‐optical detector that can be easily extended into an array for focal plane imaging applications. The quasi‐optical detector consists of an antenna‐coupled detector packaged by a low‐profile meta‐surface reflector and a 3D‐printed lens. The antenna‐coupled detector with a GaAs Schottky diode is printed on a low‐cost and low‐loss laminate. To extract the detected low‐frequency signal within a small footprint, a pair of vertical metallic posts instead of conventional planar strips is designed and loaded at the ends of the antenna. For facilitating unidirectional radiation patterns, a low‐profile meta‐surface reflector with a thickness of λg/8 is placed under the antenna‐coupled detector. In addition, a 3D‐printed dielectric lens is loaded upon the antenna‐coupled detector, which can enhance the radiation gain by 6 dB. Both the meta‐surface reflector and the 3D‐printed lens are fixed by an asymmetric H‐shaped framework, forming a low‐cost and lightweight package for the detector. Based on the proposed detector, a W‐band 1 × 16 array is experimentally demonstrated, exhibiting a responsivity of 100 V/W~410 V/W from 92 to 110 GHz. The total size of the array is only 27 λ × 4 λ × 1.8 λ, where λ is the free space wavelength at the center frequency. [ABSTRACT FROM AUTHOR]

Short-wavelength infrared (SWIR) detection systems are increasingly in demand for surveillance, reconnaissance, and remote sensing applications. Eye-safe SWIR lasers can be utilized for active imaging systems with high image contrast and long detection range. The gated-viewing (GV) technique using short-pulse lasers and fast-gated cameras in the nanosecond range enables utilizing the distance information in addition to the signal intensity of the acquired images. The InGaAs material system is very well suited for the fabrication of high-performance SWIR photodetectors providing a typical cutoff wavelength of 1.7 μm, which covers the emission lines of available laser sources at typical telecom wavelengths around 1.55 μm. However, the usually short integration times needed for GV leads to very small photosignals. We report on the development of SWIR avalanche photodetector (APD) arrays with 640 × 512 pixels and 15 μm pixel pitch based on the InGaAs material system. The InGaAs-APD focal plane arrays have been successfully integrated into SWIR cameras which yield gain values of M ≈ 10 on camera level at a reverse bias voltage around 21 V and are the first InGaAs-based SWIR cameras worldwide providing a 640 × 512 image format and utilizing avalanche gain for signal amplification. The camera performance is demonstrated by SWIR laser GV sample images. [ABSTRACT FROM AUTHOR]

The motivation of this work is to demonstrate the versatility and potential of laser processing in the fabrication of PbSe thin films and focal plane array devices. This work fabricates an FPA device with any need for the suite of equipment and chemicals necessary for photolithography and etching. Advances in laser technologies and the vast number of laser parameters available are enabling the huge potential for laser processing of thin films and device fabrication. This can be accomplished faster using lasers with fewer steps than using conventional thin film deposition and photolithography methods. This work presents the fabrication and simple operation of a proof-of-concept PbSe-based, 120-pixel PFA (10 × 12 pixel) focal plane array using only laser processing for film deposition and device patterning. Lasers were used to both deposition and pattern a PbSe film with 60 × 70 µm pixels with 100 µm pitch with a unit cell photoresponse of 17% DelR. Additional results, challenges, limitations, and suggested future improvements are presented. [ABSTRACT FROM AUTHOR]

Performance enhancement of a very inexpensive millimeter-wave (MMW)/terahertz (THz) sensor for MMW/THz imaging systems is experimentally demonstrated in this study. The MMW sensor is composed of a glow discharge detector (GDD) and a light-to-frequency (LTF) converter combination. The experimental results given in this study show an improvement in the performance parameters of the detector element, such as the minimum detectable signal, as well as the signal to noise ratio (SNR) and the noise equivalent power (NEP), when a NIR long-pass filter was inserted between the GDD and the LTF combination. A detailed derivation of the NEP of this unique sensor is presented in this work. Based on this derivation and the experimental measurements, the NEP value was calculated.