Graphene/MoS2-xOx/graphene photomemristor with tunable non-volatile responsivities for neuromorphic vision processing.

Conventional artificial intelligence (AI) machine vision technology, based on the von Neumann architecture, uses separate sensing, computing, and storage units to process huge amounts of vision data generated in sensory terminals. The frequent movement of redundant data between sensors, processors and memory, however, results in high-power consumption and latency. A more efficient approach is to offload some of the memory and computational tasks to sensor elements that can perceive and process the optical signal simultaneously. Here, we proposed a non-volatile photomemristor, in which the reconfigurable responsivity can be modulated by the charge and/or photon flux through it and further stored in the device. The non-volatile photomemristor has a simple two-terminal architecture, in which photoexcited carriers and oxygen-related ions are coupled, leading to a displaced and pinched hysteresis in the current-voltage characteristics. For the first time, non-volatile photomemristors implement computationally complete logic with photoresponse-stateful operations, for which the same photomemristor serves as both a logic gate and memory, using photoresponse as a physical state variable instead of light, voltage and memresistance. The polarity reversal of photomemristors shows great potential for in-memory sensing and computing with feature extraction and image recognition for neuromorphic vision.

An Improved Frequency Domain Guided Thermal Imager Strips Removal Algorithm Based on LRSID.

The thermal imaging image of the Sustainable Development Science Satellite (SDGSAT-1) is mainly used for high-resolution observations of the ground width, due to the influence of blind elements and non-uniformity of the detector, and the system is a pendulum sweep imaging mode, resulting in fringed noise in the image. In this paper, a Fringing algorithm based on LRSID (low-rank-based single-image decomposition) algorithm is proposed, which can effectively remove the lateral and vertical fringe noise of the thermal imager and maintain the detail and clarity of the image. First, pretreatment of the obvious light and dark stripes then, based on LLSID algorithm, the vertical direction pinstripes and horizontal stripes are processed; finally, the fringed frequency band of the original image is replaced in the frequency domain with the image frequency domain processed by the LRSID algorithm, and then the Fourier inverse transformation is performed to obtain the final image. Using the method proposed in this paper, the simulated and actual SDGSAT-1 thermal imaging camera remote sensing stripes images are removed, and the visual and quantitative indicators are compared with the processing results of other algorithms, and the results show that the proposed algorithm has the best performance to remove the stripes, which can effectively remove horizontal and vertical fringes at the same time, and retain the detail and clarity of the image.

Extrapolating distortion correction with local measurements for space-based multi-module splicing large-format infrared cameras.

Conventional distortion correction methods with the classical models, including radial, decentering, and thin prism distortions and with the interpolation template, depend heavily on the evenly distributed measurement data on the entire focal plane. However, owing to the restricted cubage of the vacuum tank and the large size of the assembled camera, there is no more extra space for the amounted large-format camera to adjust with the 2D turntable during laboratory vacuum experiment, which, accordingly, makes the collected measurement points gathered in just one module of the focal plane and eventually results in poor correction accuracy of the mentioned approaches. Here, in terms of the problems above, an extrapolating distortion correction method with local measurements for space-based multi-module splicing large-format infrared cameras was proposed in this paper. Benefiting from the polynomial model not being affected by the distribution of data, a third-order polynomial model adopted for distortion correction is solved by using local measurements and extrapolated reasonably, which guarantees the global camera calibration. Experimental results show that the mean distortion error can be corrected within 0.5 pixels. This method overcoming the deficiency of local test points can effectively improve the correction accuracy of the large-format camera and provide a new idea for global high-precision calibration of on-orbit payloads based on local measurements.

Improved Intra-Pixel Sensitivity Characterization Based on Diffusion and Coupling Model for Infrared Focal Plane Array Photodetector.

The high-precision characterization of the intra-pixel sensitivity (IPS) for infrared focal plane array (FPA) photodetector is of great significance to high-precision photometry and astrometry in astronomy, as well as target tracking in under-sampled remote sensing images. The discrete sub-pixel response (DSPR) model and fill factor model have been used for IPS characterization in some studies. However, these models are incomplete and lack the description of physical process of charge diffusion and capacitance coupling, leading to the inaccuracy of IPS characterization. In this paper, we propose an improved IPS characterization method based on the diffusion and coupling physical (DCP) model for infrared FPA photodetector, which considering the processes of generation and collection of the charge, can improve the accuracy of IPS characterization. The IPS model can be obtained by convolving the ideal rectangular response function with the charge diffusion function and the capacitive coupling function. Then, the IPS model is convolved with the beam spot profile to obtain the beam spot scanning response model. Finally, we calculate the parameters of IPS by fitting the beam spot scanning response map with the proposed DCP model based on the Trust-Region-Reflective algorithm. Simulated results show that when using a 3 µm beam spot to scan, the error of IPS characterization based on DCP model is 0.63%, which is better than that of DSPR model's 3.70%. Experimental results show that the fitting error of the beam spot scan response model based on DCP model is 4.29%, which is better than that of DSPR model's 8.31%.

On-Orbit Geometric Calibration from the Relative Motion of Stars for Geostationary Cameras.

Affected by the vibrations and thermal shocks during launch and the orbit penetration process, the geometric positioning model of the remote sensing cameras measured on the ground will generate a displacement, affecting the geometric accuracy of imagery and requiring recalibration. Conventional methods adopt the ground control points (GCPs) or stars as references for on-orbit geometric calibration. However, inescapable cloud coverage and discontented extraction algorithms make it extremely difficult to collect sufficient high-precision GCPs for modifying the misalignment of the camera, especially for geostationary satellites. Additionally, the number of the observed stars is very likely to be inadequate for calibrating the relative installations of the camera. In terms of the problems above, we propose a novel on-orbit geometric calibration method using the relative motion of stars for geostationary cameras. First, a geometric calibration model is constructed based on the optical system structure. Then, we analyze the relative motion transformation of the observed stars. The stellar trajectory and the auxiliary ephemeris are used to obtain the corresponding object vector for correcting the associated calibration parameters iteratively. Experimental results evaluated on the data of a geostationary experiment satellite demonstrate that the positioning errors corrected by this proposed method can be within ±2.35 pixels. This approach is able to effectively calibrate the camera and improve the positioning accuracy, which avoids the influence of cloud cover and overcomes the great dependence on the number of the observed stars.

Recent Progress on Electrical and Optical Manipulations of Perovskite Photodetectors.

Photodetectors built from conventional bulk materials such as silicon, III-V or II-VI compound semiconductors are one of the most ubiquitous types of technology in use today. The past decade has witnessed a dramatic increase in interest in emerging photodetectors based on perovskite materials driven by the growing demands for uncooled, low-cost, lightweight, and even flexible photodetection technology. Though perovskite has good electrical and optical properties, perovskite-based photodetectors always suffer from nonideal quantum efficiency and high-power consumption. Joint manipulation of electrons and photons in perovskite photodetectors is a promising strategy to improve detection efficiency. In this review, electrical and optical characteristics of typical types of perovskite photodetectors are first summarized. Electrical manipulations of electrons in perovskite photodetectors are discussed. Then, artificial photonic nanostructures for photon manipulations are detailed to improve light absorption efficiency. By reviewing the manipulation of electrons and photons in perovskite photodetectors, this review aims to provide strategies to achieve high-performance photodetectors.

Recent progress on infrared photodetectors based on InAs and InAsSb nanowires.

In recent years, quasi-1D semiconductor nanowires have attracted significant research interest in the field of optoelectronic devices. Indium arsenide (InAs) nanowire, a III-V compound semiconductor structure with a narrow band gap, shows high electron mobility and high absorption from the visible to the mid-wave infrared (MWIR), holding promise for room-temperature high-performance infrared photodetectors. Therefore, the material growth, device preparation and performance characteristics have attracted increasing attention, enabling high-sensitivity InAs nanowire photodetector from the visible to the MWIR at room temperature. This review starts by discussing the growth process of the low-dimensional structure and elementary properties of the material, such as the crystalline phase, mobility, morphology, surface states and metal contacts. Then, three solutions, including the visible-light-assisted infrared photodetection technology, vertical nanowire-array technology and band engineering by the growth of InAsSb nanowires with increasing Sb components, are elaborated to obtain longer cut-off wavelength MWIR photodetectors based on single InAs nanowire and its heterojunction structure. Finally, the potential and challenges of the state-of-the-art optoelectronic technologies for InAs nanowire MWIR photodetectors are summarized and compared, and preliminary suggestions for the technical development route and prospects are presented. This review mainly delineates the research progress of material growth, device fabrication and performance characterization of InAs nanowire MWIR photodetectors, providing a reference for the development of the next-generation high-performance photodetectors over a wide spectrum range.

High efficiency and fast van der Waals hetero-photodiodes with a unilateral depletion region.

Van der Waals (vdW) heterodiodes based on two-dimensional (2D) materials have shown tremendous potential in photovoltaic detectors and solar cells. However, such 2D photovoltaic devices are limited by low quantum efficiencies due to the severe interface recombination and the inefficient contacts. Here, we report an efficient MoS2/AsP vdW hetero-photodiode utilizing a unilateral depletion region band design and a narrow bandgap AsP as an effective carrier selective contact. The unilateral depletion region is verified via both the Fermi level and the infrared response measurements. The device demonstrates a pronounced photovoltaic behavior with a short-circuit current of 1.3 µA and a large open-circuit voltage of 0.61 V under visible light illumination. Especially, a high external quantum efficiency of 71%, a record high power conversion efficiency of 9% and a fast response time of 9 µs are achieved. Our work suggests an effective scheme to design high-performance photovoltaic devices assembled by 2D materials.

Portable System for Box Volume Measurement Based on Line-Structured Light Vision and Deep Learning.

Portable box volume measurement has always been a popular issue in the intelligent logistic industry. This work presents a portable system for box volume measurement that is based on line-structured light vision and deep learning. This system consists of a novel 2 × 2 laser line grid projector, a sensor, and software modules, with which only two laser-modulated images of boxes are required for volume measurement. For laser-modulated images, a novel end-to-end deep learning model is proposed by using an improved holistically nested edge detection network to extract edges. Furthermore, an automatic one-step calibration method for the line-structured light projector is designed for fast calibration. The experimental results show that the measuring range of our proposed system is 100-1800 mm, with errors less than ±5.0 mm. Theoretical analysis indicates that within the measuring range of the system, the measurement uncertainty of the measuring device is ±0.52 mm to ±4.0 mm, which is consistent with the experimental results. The device size is 140 mm × 35 mm × 35 mm and the weight is 110 g, thus the system is suitable for portable automatic box volume measurement.

Development of a polar-view Kirkpatrick-Baez X-ray microscope for implosion asymmetry studies.

The development of a polar-view Kirkpatrick-Baez microscope, fielded in the upper polar zone of the Shenguang-III laser fusion facility, is presented. With this microscope, the resolving power of polar-direction X-ray imaging diagnostics is improved, to the 3 ~5 µm scale. The microscope is designed for implosion asymmetry studies, with response energy points at 1.2 keV, 3.5 keV, and 8 keV. A biperiodic multilayer scheme is adopted to accommodate multiple implosion stages. We present the overall optical system design, target aiming scheme, characteristic composite imaging diagnostic experiments and initial results. The inertial-driven quasi-one-dimensional spherical implosions were observed from orthogonal directions with a convergence ratio of ~14.4. Fine features of the stagnating hot spot core are also resolved.

A Colloidal-Quantum-Dot Infrared Photodiode with High Photoconductive Gain.

The photodiode is a prevailing architecture for photodetection with the merits of fast response and low dark current. However, an ideal photodiode is also desired for both high responsivity and high external quantum efficiency (EQE), which may facilitate more applications. Here the photoconducting effect in a photodiode is discussed and an Au-PbS colloidal quantum dot (CQD)-indium tin oxide Schottky junction photodiode is fabricated. The long carrier lifetime and improved carrier mobility in tetrabutylammonium iodide-modified PbS CQDs cooperating with the proper band structure and an ultrashort channel in the diode enable the photodiode with high photoconductive gain, realizing an EQE of ≈400% and a responsivity (R) of 5.15 A W-1 while simultaneously achieving a response time of 110 µs and a specific detectivity of 1.96 × 1010 Jones under 1550 nm illumination. In addition, this CQD-based photodiode is stable, low cost, and compatible with complementary metal oxide semiconductor technology. All of these promise this device great potential in applications.