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In this article, we present the design procedure of modulated metasurface leaky-wave antennas (MMLWAs) to generate coaxial superposition of vortex beams with several orbital angular momentum (OAM) states. Based on the flat optics (FO) technique and aperture field estimation (AFE) method, an analytical framework is proposed to facilitate the implementation of MMLWAs generating multiple topological charges in the OAM regimen. Furthermore, using the spectral analysis that has been derived from the proposed model, we have shown that the symmetry of aperture shape can affect the purity of the mode. Also, the perfectly symmetric circular shape is introduced as an ideal choice for high-purity vortex generation. This single aperture antenna with embedded monopole feed can be an appropriate alternative to more complex vortex beam generators such as spiral phase plates and circular antenna arrays. The validity of the proposed analytical method has been studied by designing two structures with petal-like vortex beams. [ABSTRACT FROM AUTHOR]

So-called spatial web queries retrieve web content representing points of interest, such that the points of interest have descriptions that are relevant to query keywords and are located close to a query location. Two broad categories of such queries exist. The first encompasses queries that retrieve single spatial web objects that each satisfy the query arguments. Most proposals belong to this category. The second category, to which this paper's proposal belongs, encompasses queries that support exploratory user behavior and retrieve sets of objects that represent regions of space that may be of interest to the user. Specifically, the paper proposes a new type of query, the top- $k$ k spatial textual cluster retrieval ($k$ k -STC) query that returns the top- $k$ k clusters that (i) are located close to a query location, (ii) contain objects that are relevant with regard to given query keywords, and (iii) have an object density that exceeds a given threshold. To compute this query, we propose a DBSCAN-based approach and an OPTICS-based approach that rely on on-line density-based clustering and that exploit early stop conditions. Empirical studies on real data sets offer evidence that the paper's proposals can find good quality clusters and are capable of excellent performance. [ABSTRACT FROM AUTHOR]

The two-stage (TS) multibeam klystron (MBK) technology has recently attracted significant research attention due to its compactness and high-efficiency (HE) performance. However, there is still a lack of scientific research on the beam optics for such microwave power sources integrated with a postacceleration (PA) gap. In this article, a comprehensive optics study based on the newly developed 2-D optics code CGUN is conducted for the first time to demonstrate the most critical steps in the optics design process, by adopting the 400-MHz TS MBK for the future circular collider (FCC) as an example. Two specific challenges arise in this TS MBK, which are studied in this article, and solutions are given. First, due to the combination of slow electrons, impedance change from individual beamtubes into common volume, and the mild decay of the magnetic field, there are possible reflected electrons at the collector entrance. This requires an increase in the beam voltage to 80 kV, beyond the requirements from considering the output gap alone, as well as tighter control on bouncing electrons. The beam scalloping is also found to be highly sensitive to the position of the PA gap and magnetic field, which later demonstrates that large gap length and magnetic field are required. Final all-in-one particle-in-cell (PIC) simulations of this klystron equipped with this special optics design demonstrate that the specification of 1.2-MW continuous wave (CW) power is practically attainable with an efficiency of 77.5% and without the presence of reflected electrons at any point in the whole circuit. [ABSTRACT FROM AUTHOR]

Exploiting the inner-shot and inter-shot dependencies is essential for key-shot based video summarization. Current approaches mainly devote to modeling the video as a frame sequence by recurrent neural networks. However, one potential limitation of the sequence models is that they focus on capturing local neighborhood dependencies while the high-order dependencies in long distance are not fully exploited. In general, the frames in each shot record a certain activity and vary smoothly over time, but the multi-hop relationships occur frequently among shots. In this case, both the local and global dependencies are important for understanding the video content. Motivated by this point, we propose a reconstructive sequence-graph network (RSGN) to encode the frames and shots as sequence and graph hierarchically, where the frame-level dependencies are encoded by long short-term memory (LSTM), and the shot-level dependencies are captured by the graph convolutional network (GCN). Then, the videos are summarized by exploiting both the local and global dependencies among shots. Besides, a reconstructor is developed to reward the summary generator, so that the generator can be optimized in an unsupervised manner, which can avert the lack of annotated data in video summarization. Furthermore, under the guidance of reconstruction loss, the predicted summary can better preserve the main video content and shot-level dependencies. Practically, the experimental results on three popular datasets (i.e., SumMe, TVsum and VTW) have demonstrated the superiority of our proposed approach to the summarization task. [ABSTRACT FROM AUTHOR]

This article describes the design of the 18 m shaped offset Gregorian reflector system for the Next Generation Very Large Array (ngVLA) radio interferometer and the associated 1.66:1 axially corrugated conical horn antennas. A parametric sweep determined feed horns with the goal of pattern symmetry and low spillover efficiency. Given these feeds, a mapping function for the shaped offset Gregorian reflector system was then determined, by a full-factorial design, to achieve maximum receiving sensitivity with secondary parameters such as plate scale, scan loss, sidelobe, and cross-polarization at acceptable levels. A subreflector extension is included in a feed-down tipping configuration with improved performance over the feed-up case. The resultant optics and feeds achieve very symmetrical patterns with an aperture efficiency of around 95%, a plate scale of 15 arcsec/mm, and first and second sidelobe levels of −18 and −24 dB, respectively. The receiving sensitivity at 30 GHz is 8.7 m2/K and it increases to above 12 m2/K at 12.3 GHz and reduces to 1.5 m2/K at 116 GHz (ignoring the efficiency loss due to nonideal reflector surfaces). These sensitivities are close to the theoretical optimum. [ABSTRACT FROM AUTHOR]

Cross-domain scene classification identifies scene categories by learning knowledge from a labeled data set (source domain) to an unlabeled data set (target domain), where the source data and the target data are sampled from different distributions. A lot of domain adaptation methods are used to reduce the distribution shift across domains, and most existing methods assume that the source domain shares the same categories with the target domain. It is usually hard to find a source domain that covers all categories in the target domain. Some works exploit multiple incomplete source domains to cover the target domain. However, in such setting, the categories of each source domain are a subset of the target-domain categories, and the target domain contains “unknown” categories for each source domain. The existence of unknown categories results in the conventional domain adaptation unsuitable. Known and unknown categories should be treated separately. Therefore, a separation mechanism is proposed to separate the known and unknown categories in this article. First, multiple-source classifiers trained on the multiple source domains are used to coarsely separate the known/unknown categories in the target domain. The target images with high similarities to source images are selected as known categories, and the target images with low similarities are selected as unknown categories. Then, a binary classifier trained using the selected images is used to finely separate all target-domain images. Finally, only the known categories are implemented in the cross-domain alignment and classification. The target images get labels by integrating the hypotheses of multiple-source classifiers on the known categories. Experiments are conducted on three cross-domain data sets to demonstrate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

While the capacity of the next-generation access network is expected to be 100 Gb/s and beyond, coherent optics is going to be a logical choice for the physical layer as the currently used intensity-modulation/ direct-detection technology will fail to meet the required power budget of such high line-rate systems. In this article, we present an overview of necessities, timeframe, and technological challenges for the future passive optical network utilizing coherent technology. [ABSTRACT FROM AUTHOR]

In this work, a high-performance stripe-shaped light-emitting diode (LED) with a size of $7500\times 300\,\,\mu \text{m}^{{2}}$ is reported. With the optimized electrode design, the current can be evenly injected into the elongated chip, achieving a uniform light distribution without the use of external optics. Compared with the conventional cubic LED, the light output performance of the stripe-shaped LED (S-LED) at high current levels is significantly improved, which is mainly due to the enhanced heat dissipation. White light emission is also demonstrated by covering the chip with the yellow phosphor film. With the advantages of reduced luminous exitance, uniform illumination, and improved light output, the S-LEDs are not only suitable for various lighting applications but can also be used as backlight units for display panels. [ABSTRACT FROM AUTHOR]

In this article, types of broadband focusing lens are presented based on the ray inserting method (RIM) in the $Ku$ -band. The realizable inhomogeneous isotropic dielectric media is obtained to converge wavefront produced by a source on a focal point. The proposed three lenses are broadband because of good matching to the source and the surroundings. The finite-difference time-domain (FDTD) scheme and the full-wave simulation are used to confirm the results in the $Ku$ -band. To validate designed lenses’ performance, the circular focusing lens is realized and fabricated. The results of simulations and experiments indicate good performances of the designed lens in the wide frequency bandwidth. [ABSTRACT FROM AUTHOR]

Inspired by the background adaptive mechanism of eagle vision in different hunting environment, a biological eagle-eye vision adaptation mechanism algorithm is proposed for unmanned aerial vehicle (UAV) to detect the long-distance maritime small target in complex and changeable sea environment. First, the various environment adjustment abilities are summarized according to the physiological structures and characteristics of eagle vision. Second, the mathematical models of glaring adaptation, dim adaptation, color adaptation, and the background adaptation are established based on the background adaptation mechanisms of eagle vision. Last but not least, our proposed biological eagle-eye vision adaptation method and other five comparative experiments are implemented in different scenes, such as dazzling, cloudy, dusk, etc. The results of various evaluation indices show that the information of maritime small target is retained satisfactorily and the background of sea or sky is restrained effectively by the proposed algorithm. The maritime small target detection algorithm can be used for the vision system of UAV operating on the sea. It provides a feasible solution for UAV's remote vision autonomous navigation in changeable sea environment. [ABSTRACT FROM AUTHOR]

This article describes two novel perturbation solutions for the electromagnetic analysis of eccentric coaxial waveguides. Different techniques have been used for solving this type of problem in the past. Most of them rely on solving a complicated transcendental equation obtained from the Graf’s addition theorem or on brute-force numerical methods such as finite differences and finite elements. The proposed approach, instead, employs transformation optics to map the original problem into a problem consisting of a concentric coaxial waveguide filled with an anisotropic and inhomogeneous medium. The corresponding (transformed) wave equation is then solved via a regular perturbation series. This method allows to compute field and wavenumber corrections of the transverse magnetic (TM) and transverse electric (TE) modes for coaxial waveguides with small eccentricities. In addition, another solution is obtained by using the cavity-material perturbation approach for providing the cutoff wavenumbers of TM and TE fields. The proposed perturbation solutions are validated against full-wave finite-element and finite-volume results in several examples. [ABSTRACT FROM AUTHOR]

Contribution: A do-it-yourself (DIY) light wave sensing (LWS) and communication project was developed to generate interest and clarify basic electromagnetic (EM) and wireless sensing/communication concepts among students at different education levels from middle school to undergraduate. This article demonstrates the nature of the project and its preliminary effectiveness. Background: Concepts in wireless sensing and communication are generally considered hard to comprehend being underpinned only by theoretical coursework and occasional simulations. Further, K–12 schools and small academic institutions may not have the resources necessary to produce tangible demonstrations for clarification. The consequent lack of affordable hands-on experiences fails to motivate and engage students. Intended Outcomes: The DIY-LWS is intended to make wireless concepts more understandable and less esoteric by linking fundamental concepts with student-relevant technologies, such as solar cells, visible lights, and smartphones. It is also intended to pique student interest by allowing them to personally assemble, operate, and explore a light-based wireless communication system. Students complete assessments before and after the project to quantify its effectiveness. Application Design: A preliminary assessment is used to determine the student base knowledge level and enthusiasm for wireless and related core topics. Students are instructed to assemble and test their own DIY-LWS hardware to provide a hands-on experience and stimulate further exploration. Short lectures are given to link conceptual ideas to the real-world phenomena students personally observed. Finally, students are reassessed to quantify any change in conceptual understanding. Findings: The DIY-LWS kits have been used in multiple events with students at different levels from secondary to high schools to college. As part of a triangulated assessment methodology, pre- and post-assessments revealed pronounced improvements (the number of correct answers doubled) in student understanding of EM concepts. Instructors observed tremendous interest and excitement among the students during and after the experiments. [ABSTRACT FROM AUTHOR]

We present the first results of a custom low-noise silicon photodiode detector designed for use with X-ray capillary optics. This system is intended to perform as a smaller, lighter, and low-powered alternative to currently existing X-ray telescope technologies. The detector has an active area with a diameter of 100 $\mu \text{m}$ , and its small size leads to a low capacitance of well under 1 pF and a leakage current of 1 pA or less at the depletion voltage. We tested the detector with both a discrete preamp and an ultralow-noise front-end application-specific integrated circuit (ASIC). The front-end ASIC, developed at Brookhaven National Laboratory, was designed for low-capacitance detectors but had not been previously tested with a detector. Here, we discuss the detector design, the experimental setup, and the resulting detector performance. Using radioactive laboratory sources, we measure a full-width at half-maximum (FWHM) of 211 ± 8 eV at 5.9 keV with the ASIC and are able to set the threshold as low as 0.6 keV. [ABSTRACT FROM AUTHOR]

This work is to investigate the instrumentation implementing issues of back focal plane (BFP)-typed apertometer. Firstly, we introduce a general instrument architecture of the BFP-typed apertometer, including the hardware (optics and mechanics) of the system, operation procedures of control and measurement system, and also the digital image processing algorithm/software. Secondly, we are the first to discuss the gradual rising effect of total-internal-reflection (TIR) phenomenon, the criteria on how to “exactly” locate the reference ring on BFP images, and the corresponding accuracies. As a significantly important complement, we further discuss three important issues: 1) the influence of Goos–Hänchen shift on numerical aperture (NA) measurement; 2) comparison of one-dimension and two-dimension identification algorithms; and 3) comparison of center locating using Fourier correlation analysis (FCA) and Hough transformation (HT) algorithms. [ABSTRACT FROM AUTHOR]

In this article, a Shack–Hartmann wavefront sensor is combined with a mechatronic positioning system to overcome the limited dynamic range of the Shack–Hartmann sensor (SHS) by repositioning and reorienting the SHS. Feedback loops to ensure a tangential orientation of the wavefront sensor in every measurement position and a measurement strategy that compensates for tip and tilt between wavefront and sensor are described and implemented. A framework that estimates the admissible measurement trajectories by relating the positioning errors caused by misalignments of the stages to the parameters of the wavefront sensor is developed. It is demonstrated that the setup is capable of directly measuring a highly divergent optical wavefront by combining wavefront data and positioning data acquired along the wavefront generated by a microscope objective with numerical aperture (NA) of 0.45. [ABSTRACT FROM AUTHOR]

Depth of field is an important factor of imaging systems that highly affects the quality of the acquired spatial information. Extended depth of field (EDoF) imaging is a challenging ill-posed problem and has been extensively addressed in the literature. We propose a computational imaging approach for EDoF, where we employ wavefront coding via a diffractive optical element (DOE) and we achieve deblurring through a convolutional neural network. Thanks to the end-to-end differentiable modeling of optical image formation and computational post-processing, we jointly optimize the optical design, i.e., DOE, and the deblurring through standard gradient descent methods. Based on the properties of the underlying refractive lens and the desired EDoF range, we provide an analytical expression for the search space of the DOE, which is instrumental in the convergence of the end-to-end network. We achieve superior EDoF imaging performance compared to the state of the art, where we demonstrate results with minimal artifacts in various scenarios, including deep 3D scenes and broadband imaging. [ABSTRACT FROM AUTHOR]

Modern FPGA accelerators can be equipped with many high-bandwidth network I/Os, e.g., 64 x 50 Gbps, enabled by onboard optics or co-packaged optics. Some dozens of tightly coupled FPGA accelerators form an emerging computing platform for distributed data processing. However, a conventional indirect packet network using Ethernet's Intellectual Properties imposes an unacceptably large amount of the logic for handling such high-bandwidth interconnects on an FPGA. Besides the indirect network, another approach builds a direct packet network. Existing direct inter-FPGA networks have a low-radix network topology, e.g., 2-D torus. However, the low-radix network has the disadvantage of a large diameter and large average shortest path length that increases the latency of collectives. To mitigate both problems, we propose a lightweight, fully connected inter-FPGA network called OPTWEB for efficient collectives. Since all end-to-end separate communication paths are statically established using onboard optics, raw block data can be transferred with simple link-level synchronization. Once each source FPGA assigns a communication stream to a path by its internal switch logic between memory-mapped and stream interfaces for remote direct memory access (RDMA), a one-hop transfer is provided. Since each FPGA performs input/output of the remote memory access between all FPGAs simultaneously, multiple RDMAs efficiently form collectives. The OPTWEB network provides 0.71-μsec start-up latency of collectives among multiple Intel Stratix 10 MX FPGA cards with onboard optics. The OPTWEB network consumes 31.4 and 57.7 percent of adaptive logic modules for aggregate 400-Gbps and 800-Gbps interconnects on a custom Stratix 10 MX 2100 FPGA, respectively. The OPTWEB network reduces by 40 percent the cost compared to a conventional packet network. [ABSTRACT FROM AUTHOR]

For an improved reduction of thermally induced wavefront aberrations associated with the projection lens in deep ultraviolet lithography, this article proposes a regularization-based recursive linear estimation strategy for the model parameters of a predictive control scheme. The linearity of estimation is ensured by estimating only the gains of an approximate exponential regression model that effectively describes the spatial cooling behavior, where the time constants are preset to specific values such that the actual exponentials are collectively well described. Owing to its suitability for recursive formulations, the corresponding solution involves the celebrated Tikhonov regularization, with its regularization term additionally consisting of a scaling term that relates to the magnitudes of parameters so that the same regularization parameter can be used at different exposure settings and time moments. Moreover, for a proper tuning of this regularization parameter, the method of generalized cross-validation is adopted. By means of comparative analysis with respect to both synthetic and real data, the treated method is demonstrated to outperform the traditional Kalman filter, as well as nonlinear approaches such as the extended and unscented Kalman filters. [ABSTRACT FROM AUTHOR]

A concept of achieving trifocal terahertz (THz) radiation is discussed based on the application of a periodic electric field in addition to two dark hollow laser beams impinging into collisional plasma. Nonlinear plasma medium is engineered for altering the dynamics of electrons under such a periodic electric field and obtaining an additional transverse component of nonlinear current. This additional component modifies the optics associated with the emitted radiation, leading to trifocal THz radiation. The parameters associated with the doughnut intensity of dark hollow laser beams, such as beamwidth and beam order, control the position and peak of the emitted THz field. Interestingly, the efficiency of the emitted THz field can also be tuned by appropriate combinations of the laser beam orders. [ABSTRACT FROM AUTHOR]

Contribution: A hybrid approach involving reduced lecture content with project-based learning (PBL) was introduced to a standalone course in optics at an engineering school not specialized in this area, with promising results. Background: At most schools, optics is an elective “niche” area involving a single senior course. This presents challenges, since the topic has breadth and depth, leaving little time for application projects. Yet, seniors want future applicability. After many years, the instructor questioned his “broad-brush” approach involving many topics with limited application, especially given the role of optics and photonics in technology leadership. A literature search uncovered recent use of project-based methods for optics in K–12 and community colleges but little use in U.S. universities, suggesting an opportunity. Intended Outcomes: The authors intended that achievement and valuation by students would be greater with authentic projects and less content. Application Design: Therefore, an approach that concentrated content and project work on light’s dualistic nature in a mathematically rigorous manner was taken. With reduced content, class time was available for PBL, whereby the problem motivated the content. For light’s wave nature, five lecture weeks were followed by a project simulating the propagation of light. For the particle nature, a circuit design project to implement analog electronic circuits during class occurred after five lecture weeks. Findings: Student interviews and instructor perspectives on impacts of learning, career preparation, graduate school interest, and in-class engagement uncovered encouraging results. A direct assessment showed significantly higher homework scores with the course changes. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel non-parametric clustering technique. Our technique is based on the notion that each latent cluster is comprised of layers that surround its core, where the external layers, or border points, implicitly separate the clusters. Unlike previous techniques, such as DBSCAN, where the cores of the clusters are defined directly by their densities, here the latent cores are revealed by a progressive peeling of the border points. Analyzing the density of the local neighborhoods allows identifying the border points and associating them with points of inner layers. We show that the peeling process adapts to the local densities and characteristics to successfully separate adjacent clusters (of possibly different densities). We extensively tested our technique on large sets of labeled data, including high-dimensional datasets of deep features that were trained by a convolutional neural network. We show that our technique is competitive to other state-of-the-art non-parametric methods using a fixed set of parameters throughout the experiments. [ABSTRACT FROM AUTHOR]

This article describes the design and prelaunch performance of the antenna subsystem of the low-cost 118.75 GHz temperature sounding radiometer payload used in the PolarCube and GEMS-IOD 3U CubeSat missions. Radiometric sounding measurements used for providing data for weather prediction are strongly affected by the main beam, ohmic, and spillover efficiencies of the optics, as well as by inhomogeneities in the scene and background radiation fields. The interpretation of radiometric data is affected by the accuracy with which these antenna efficiencies can be determined, particularly for radiometers that do not permit full main beam external calibration. To this end, an HE11 mode full wave Fourier–Bessel electromagnetic field analysis was developed for determination of an optimal feed horn and reflector geometry such that the main beam and spillover efficiencies of the system are maximized, and these and the antenna phase center location that maximizes phase efficiency are precisely known. The efficacy of employing a sub-millimeter wave 3-D-printed corrugated conical horn operable between 110 and 127 GHz as the feed for an offset paraboloidal reflector due to its very low cost and rapid manufacturability is also addressed. Horn measurements indicate a reflection coefficient below −15 dB and far-field radiation patterns that compare closely to simulation. Although there is some asymmetry in the horn pattern, the average main beam efficiency is 89% for a main reflector subtending a 16° half-angle. Initial performance obtained from airborne measurements over Antarctica on the NASA DC-8 during Operation IceBridge in Oct–Nov 2016 suggests a well-focused scanning antenna subsystem. After final payload assembly, the antenna’s 3 dB beamwidth extracted from a bridge-scan field experiment was broader by ~ 0.1° compared with the idealized simulated pattern. [ABSTRACT FROM AUTHOR]

Cross-domain scene classification refers to the scene classification task in which the training set (termed source domain) and the test set (termed target domain) come from different distributions. Various domain adaptation methods have been developed to reduce the distribution discrepancy between different domains. However, current domain adaptation methods assume that the source domain and target domain share the same categories. In reality, it is hard to find a source domain that can completely cover all the categories of target domain. In this article, we propose to use multiple complementary source domains to form the categories of target domain. A multisource compensation network (MSCN) is proposed to tackle these challenges: distribution discrepancy and category incompleteness. First, a pretrained convolutional neural network (CNN) is exploited to learn the feature representation for each domain. Second, a cross-domain alignment module is developed to reduce the domain shift between source and target domains. Domain shift is reduced by mapping the two domain features into a common feature space. Finally, a classifier complement module is proposed to align categories in multiple sources and learn a target classifier. Two cross-domain classification data sets are constructed using four heterogeneous remote sensing scene classification data sets. Extensive experiments are conducted on these datasets to validate the effectiveness of the proposed method. The proposed method can achieve 81.23% and 81.97% average accuracies on two-source-complementary data set and three-source-complementary data set, respectively. [ABSTRACT FROM AUTHOR]

Non-Hermitian systems characterized by suitable spatial distributions of gain and loss can exhibit “spectral singularities” in the form of zero-width resonances associated with real-frequency poles in the scattering operator. Here, we study this intriguing phenomenon in connection with cylindrical geometries and explore possible applications to controlling and tailoring in unconventional ways the scattering response of subwavelength- and wavelength-sized objects. Among the possible implications and applications, we illustrate the additional degrees of freedom available in the scattering–absorption–extinction tradeoff and address the engineering of zero-forward scattering, transverse scattering, and gain-controlled reconfigurability of the scattering pattern, also paying attention to stability issues. Our results may open up new vistas in active and reconfigurable nanophotonics platforms. [ABSTRACT FROM AUTHOR]

Solar simulators are a fundamental instrument to characterize solar cells parameters, as they can reproduce the operating conditions under which the solar cells are going to work. However, these systems are frequently big, heavy, and expensive, and a small solar simulator could be a good contribution to test small prototyping devices manufactured in research labs, especially if it could manage the irradiation at any wavelength interval in a custom way. We have designed, developed, and calibrated a small solar simulator made entirely with LEDs, no optics inside, and electronically controlled through a PC using an Arduino microcontroller. The whole structure is 3-D printed in black PLA plastic. The electrical current through the LEDs, and thus the spectral irradiance of the simulator, is controlled with a very intuitive LabVIEW interface. As our calibration proves, we have built an easily reproducible and low-cost Class AAA solar simulator in a central illumination area of 1 cm2, according to the IEC60904-9 standard. This means that the homogeneity in that area is under a 2% deviation in spatial terms, below 0.5% in temporal terms, and is a factor of a 3% close to the AM1.5G sun reference spectrum. The system can be built and used in any research lab to get quick tests of new small solar cells of any material. [ABSTRACT FROM AUTHOR]

A novel highly linear magnetless isolator based on weakly coupled nonreciprocal metamaterials is proposed in this article. Nonreciprocal devices, such as isolators and circulators, are widely used in modern microwave, optics. Nowadays, nonreciprocity is exclusively achieved with anisotropic magneto-optic material. Unfortunately, this material needs permanent magnetic bias and is typically bulky, which remains incompatible with technology for integrated circuit. In this article, we reveal that strong isolation can be achieved even under the weak coupling between the transmission line and magnetless nonreciprocal metamaterials (MNMs). Compared with previous magnetless nonreciprocal approaches, in this article, as the wave propagates from port 2 to port 1, the interaction between the incoming wave and nonlinear devices can be neglected due to the weak coupling, yielding low loss (|S12| = −1.03dB) and high linearity $({P}_{{1dB}}{>{17} {dBm}}$ , ${{OIP}}_{{3}}{=33.5 {dBm})}$. As the wave propagates from port 2 to port 1, 36.2 – dB isolation can be achieved under the loop resonance. Furthermore, the frequency reconfiguration of MNMs has been investigated for the first time, leading to broadband and multiband isolators. [ABSTRACT FROM AUTHOR]

In human–robot coexisting environment, one of the primary objectives is to equip robots with the facilities of detecting and following a human being in front, using various sensors. Within this genre, developing algorithms for vision sensor-based shoe detection and subsequently following is considered an active problem. Considering that the shoe poses, during the pursuit, undergo different transformations, this paper presents how the vision sensor based shoe detection problem can be treated as analogous to template matching under general conditions. This paper first shows how a popular fast randomized template-matching algorithm, called FAsT-Match algorithm, and its contemporary variant for color images, called CFAsT-Match algorithm, can be implemented in real robots with success for detecting shoes in subsequent frames. Then, this paper proposes a new density-based clustering method, called ordering points to identify the clustering structure (OPTICS), based template-matching algorithm that is specifically developed to overcome several implementation problems associated with the FAsT-Match and CFAsT-Match algorithms, in real life. Experimental results and performance evaluations demonstrate the superiority of the proposed OPTICS-based algorithm for shoe detection during human tracking in human–robot coexisting environments. [ABSTRACT FROM AUTHOR]

An approach to design a hyperbolic lenslet for mid-infrared nanofocusing based on fragmented high-order transformation optics (TO) (FHTO) method is proposed, which can be realized with binary realistic metal and dielectric nanolayers. The conceptual idea is achieved by discretizing the lenslet into $N(N>1)$ concentric fragments and perform high-order TO in each fragment with different values of azimuthal $s$ parameter — an unconstrained parameter that defines the operation point of the nanofocusing device. To highlight the superior performance of using the FHTO in the nanofocusing versus the unitary $(N=1)$ high-order TO (UHTO), both methods are adopted to design the hyperbolic lenslet. The numerical simulation results show that the FHTO (e.g., $N\to \infty $ and $N = 5$) exhibits superior focusing performance compared with the UHTO. For example, the performance of the FHTO is better than that of the UHTO by ~2.5 (5.3) times in spectral resolution (power throughput). Remarkably, even the manufacturable lenslet designed using FHTO-approach with realizable number of metal-dielectric binary layers (five pairs) demonstrates superior performance than the UHTO. It is noteworthy to mention that the design of FHTO-based devices enabled by circular effective-medium theory (CEMT) provides a means to bridge the gap between theoretical design and practical realization of nanophotonics systems. [ABSTRACT FROM AUTHOR]

Defective die on a wafer map tend to cluster in distinguishable patterns, and such defect patterns can provide crucial information to identify equipment problems or process failures in the semiconductor manufacturing. Therefore, it is important to accurately and efficiently classify the defect patterns. In this paper, we propose a novel clustering-based defect pattern detection and classification framework for wafer bin map (WBM). The proposed framework has many advantages. Outlier detection and defect cluster pattern extraction can be done at the same time; arbitrarily shaped cluster patterns can be detected; and there is no need to specify the number of clusters in advance. Based on WBM property, the parameters used in the clustering algorithm are fixed so that parameter sensitivity can be avoided. Since the defect patterns are classified based on extracted features, no labeled data and no supervised classification training are needed and single-type patterns as well as mixed-type patterns can be found. Extensive experiments conducted on a real-world WM-811K dataset has shown the superiority of proposed framework. The proposed framework can also be used in a big data environment to accelerate performance. [ABSTRACT FROM AUTHOR]

Retinal template matching and registration is an important challenge in teleophthalmology with low-cost imaging devices. However, the images from such devices generally have a small field of view (FOV) and image quality degradations, making matching difficult. In this paper, we develop an efficient and accurate retinal matching technique that combines dimension reduction and mutual information (MI), called RetinaMatch. The dimension reduction initializes the MI optimization as a coarse localization process, which narrows the optimization domain and avoids local optima. The effectiveness of RetinaMatch is demonstrated on the open fundus image database STARE with simulated reduced FOV and anticipated degradations, and on retinal images acquired by adapter-based optics attached to a smartphone. RetinaMatch achieves a success rate over 94% on human retinal images with the matched target registration errors below 2 pixels on average, excluding the observer variability, outperforming standard template matching solutions. In the application of measuring vessel diameter repeatedly, single pixel errors are expected. In addition, our method can be used in the process of image mosaicking with area-based registration, providing a robust approach when feature-based methods fail. To the best of our knowledge, this is the first template matching algorithm for retina images with small template images from unconstrained retinal areas. In the context of the emerging mixed reality market, we envision automated retinal image matching and registration methods as transformative for advanced teleophthalmology and long-term retinal monitoring. [ABSTRACT FROM AUTHOR]

Hyperspectral images (HSIs) convey more useful information than RGB or gray images, which are widely used in many remote sensing tasks. In real scenarios, HSIs are inevitably corrupted by noise because of sensors’ imperfectness or atmospheric influence. Recently, many HSI denoising methods have been proposed to utilize the interband information between different spectral bands. However, these methods regard the HSI as a whole and treat the different spectral bands with the same noise level. In fact, the noise levels in different bands are different. Especially, only few certain bands are corrupted by noise, named the target noised bands. Under this circumstance, an HSI denoising method is proposed by considering the band relationship and different noise levels. The target noised bands are adaptively denoised by fusing some selected bands. Specifically, some related but quality superior bands are selected according to the target noised bands. Then, the target noised bands can be denoised by fusing the selected related bands. Experimental results show that the proposed method achieves considerable performances in comparison with several state-of-the-art hyperspectral denoising methods. [ABSTRACT FROM AUTHOR]

This paper investigates the generation of Laguerre–Gaussian (LG) modes at radio frequencies (RFs) by utilizing either a continuous aperture or a discrete array. The mode generation can be performed with or without sidelobe control, and superdirectivity is avoided by properly selecting the system geometry and regularizing the associated inverse problem. For an individual mode, a continuous aperture source is first determined based on the singular value decomposition of the wave system. This continuous source is subsequently discretized following the construction of a 2-D quadrature rule, which, in the two extreme cases of no and maximum sidelobe suppression, results in an array grid that inherently requires a minimum number of antenna elements. A tradeoff can be made between the adopted array element number and the realized sidelobe level. A method to use a single array with a conserved number of elements to generate and multiplex multiple modes simultaneously is also developed. Full-wave simulations are used to demonstrate the application of the developed theories to arrays of realistic antennas with mutual coupling included. The study shows that, despite their origin in optics, LG modes can be accurately generated in the RF regime, and therefore still play a crucial role in orbital angular momentum (OAM)-based radio. [ABSTRACT FROM AUTHOR]

A complete framework for the linear time-invariant (LTI) filtering theory of bivariate signals is proposed based on tailored quaternion Fourier transform. This framework features a direct description of LTI filters in terms of their eigenproperties enabling compact calculus and physically interpretable filtering relations in the frequency domain. The design of filters exhibiting fundamental properties of polarization optics (birefringence and diattenuation) is straightforward. It yields an efficient spectral synthesis method and new insights on Wiener filtering for bivariate signals with prescribed frequency-dependent polarization properties. This generic framework facilitates original descriptions of bivariate signals in two components with specific geometric or statistical properties. Numerical experiments support our theoretical analysis and illustrate the relevance of the approach on synthetic data. [ABSTRACT FROM AUTHOR]

In order to reconstruct the plasma boundary directly and independently, a new method based on visible imaging diagnostics is developed for experimental advanced superconducting tokamak (EAST); its effectiveness has been verified by conducting offline experiments based on EAST’s historical data. The offline boundary reconstruction results, including X-points, are compared to offline equilibrium fitting code (offline EFIT), which is a commonly used reconstruction method. With an average error of 1.5 cm, the total processing time for one frame is less than 2 ms by current software and hardware. When the camera sensor is not saturated, the algorithm is robust for different image intensities of the plasma discharge. The results of the boundary reconstruction by visible imaging diagnostics also show potential for real-time plasma control in a tokamak. [ABSTRACT FROM AUTHOR]

Computational imaging techniques allow capturing richer, more complete representations of a scene through the introduction of novel computational algorithms, overcoming the limitations imposed by hardware and optics. The areas of application range from medical imaging to security, to areas in engineering, to name a few. Computational displays combine optics, hardware and computation to faithfully reproduce the world as seen by our eyes, something that current displays still cannot do. This article looks at a few examples of both, aiming to convey the power of the joint co-design of hardware and computational algorithms, also taking into account visual perception. [ABSTRACT FROM PUBLISHER]

Optical flow calculation algorithms are hard to implement on the hardware level in real-time, due to their complexity and high computational load. Therefore, presented works in the literature focusing on the hardware implementation are limited. In this paper, we present a hierarchical block matching-based optical flow algorithm suitable for real-time hardware implementation. The algorithm estimates the initial optical flow with block matching and refines the vectors with local smoothness constraints in each level. We evaluate the proposed algorithm with novel data sets and provide results compared with the ground truth optical flow. Furthermore, we present a reconfigurable hardware architecture of the proposed algorithm for calculating the optical flow in real-time. The presented system can process $640\times 480$ resolution frames at 39 frames/s. [ABSTRACT FROM PUBLISHER]

In this paper, we construct discrete fractional Fourier transforms (DFrFT) using recently introduced closed-form Hermite–Gaussian-like (HGL) eigenvectors. With respect to such eigenvectors, we discuss the convergence of their components to samples of the corresponding continuous Hermite–Gaussian functions and propose solutions to deal with some restrictions related to their construction. This allows us to give new procedures for obtaining orthonormal bases of HGL eigenvectors, which are used to fractionalize the discrete Fourier transform. We illustrate the application of the resulting DFrFT in the scenario of filtering in the fractional domain and compare the results with existing DFrFT approaches. [ABSTRACT FROM PUBLISHER]

We report on the pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal. The compressed pulse energy is 4.5~\mu \textJ , which corresponds to 84 W of average power, with a compression efficiency of 88%. This recently introduced compression scheme is suitable for a large pulse energy range and for high average power. In this paper, we show that it can achieve three times shorter pulses than previously demonstrated. [ABSTRACT FROM AUTHOR]

Zero-intermediate frequency (IF) receiver features the advantages of compact structure and agile operating frequency, but faces the problems of local oscillator (LO) leakage, direct current (dc) offset, even-order distortion, and in-phase/quadrature (I/Q) imbalance. In this paper, a photonic microwave I/Q mixer for zero-IF receiver is proposed based on a single integrated polarization multiplexing Mach–Zehnder modulator (PDM-MZM). Thanks to its all-optical operation and LO power optimization, an I/Q phase imbalance below 0.9°, an isolation ratio below −30 dB, and a typical conversion gain of −2.3 dB are achieved over an ultra-wide operating frequency from 10 to 40 GHz. Combined with the balanced detection techniques, the dc offset and even-order distortions are well suppressed, and the typical third-order spurious free dynamic range is 107.9 dB $\cdot $ Hz ^{2/3} . Using the proposed photonic I/Q mixer, the vector signals with various modulation formats, carrier frequencies, and data rates (200–700 Mb/s) are directly demodulated to I/Q basebands, and the error vector magnitude and the bit rate error are measured with the power range from −25 to 15 dBm. Subharmonic vector I/Q demodulation is also experimentally demonstrated. The proposed all-optical, ultra-wideband and high-efficient microwave I/Q mixer is suitable for a zero-IF receiver and may find potential applications in electronic systems such as wideband wireless communications, frequency-hopping radar, or multiband satellite transponder. [ABSTRACT FROM PUBLISHER]

We report a 30-GHz impulse radiator chip for high-resolution 3-D radar imaging. In this paper, an asymmetrical topology in the cross-coupled pulsed VCO is introduced to minimize timing jitter of radiated impulses to 178 fs, which enables highly efficient spatial combining. The coherent combining over the air has been performed with two widely spaced impulse radiators. The shortest full-width-at-half-maximum pulsewidth of 60 ps is recorded. 3-D images of various metallic objects and dielectric objects are produced using a custom-designed synthetic array imaging system. A depth resolution of 9 mm and a lateral resolution of 8 mm at a range of 10 cm have been achieved. The impulse radiator was implemented in a 130-nm SiGe BiCMOS process technology with an area of 2.85 mm2 and an average power consumption of 106 mW. [ABSTRACT FROM PUBLISHER]

Breaking through diffraction limit at terahertz frequencies is currently performed with the near-field scanning optical microscopy, which suffers from low integration and sensitivity limitations. In this paper, a solid-state superresolution imaging device in 130-nm SiGe BiCMOS technology operating around 534–562 GHz is presented. The device exhibits a single-chip integration of the complete imaging functionality, including a tunable CW illumination source, near-field sensing, and power detection with a high response of up to 9.65 \mu \textA and a noise-equivalent power of around 15–21 pW /\sqrt \text Hz at 60 kHz. Here, the stopband characteristics of a novel cross-bridged double split-ring resonator are exploited as an object-tunable transmission gate between a 3-push Colpitts oscillator and a simple HBT power detector. The resonator features a 3-D topography to achieve high-spatial confinement of the surface near-fields and is capable of resolving structural details with an estimated lateral resolution down to 10–12 \mu \textm . For a separate antenna-coupled oscillator breakout, a radiated power of up to 28.2 \mu \textW was measured. Furthermore, a 2-D raster-scanned superresolution image with a remarkable signal-to-noise ratio of 42 dB was captured for the device operating even at dc. [ABSTRACT FROM PUBLISHER]

A system scheme is presented, which allows non-reciprocal wave transmission or directional amplification of electromagnetic signals, using a boxed four-node method. Edges represent strong hopping interactions and diagonals stand for weak parametric interactions. Using careful optimization of values for design parameters, we are able to obtain non-reciprocity in excess of 12 and 130 dB for intrinsic and extrinsic configurations at identical input/output frequencies. For the directional amplification, an isolation as high as 40 dB is demonstrated with the forward/backward gains of ±20 dB. Cascading two such systems potentially can offer high isolations at high gains. [ABSTRACT FROM AUTHOR]

A tetrahedron meshing and transforming method for 3-D implementation of transformation optics is proposed and verified for a few waveguide components. The method is applicable to a wide range of electromagnetic problems. An important feature of the proposed method is that the transformed medium will be piecewise homogeneous and free of any singularities. In this method, the region under transformation is divided into a few tetrahedrons, both in the physical and virtual domains. Each tetrahedron of the physical domain transforms to a tetrahedron in the virtual domain. The material properties of each tetrahedron are then calculated using the Jacobean matrix of the transformation. Since the elements of the Jacobean matrix are constant, the $\varepsilon$ and $\mu$ tensors are finite and homogeneous in each tetrahedron. The method is verified for several rectangular waveguide coupler examples. Features of the $\varepsilon$ and $\mu$ tensors of the discussed examples are described. For instance, it is shown that the material properties may reduce to 2-D material types, or material anisotropy may reduce, under certain conditions. [ABSTRACT FROM AUTHOR]

In this paper, single-layer transmission-type metasurfaces are proposed to generate a converged vortex beam and vortex beams with different topological charges. A new metasurface design is used to generate the vortex beam, in which the required accumulated phase difference along the propagation path is realized by designing and arranging artificial single-layer unit cells. Furthermore, the converged vortex beam is generated by metasurface that superimposes the phase distribution for the vortex beam and converged beam. The transmitted efficiency of the metalens can reach 20% as designed, which approaches to the efficiency limit of this type of metasurface. [ABSTRACT FROM AUTHOR]

The theory of characteristic modes (TCMs) based on the surface integral equation (SIE) formalism is presented for the analysis of plasmonic nanostructures. With TCM, excitation-independent characteristic solutions of the underlying electromagnetic field problem are obtained. Both single and multiple particle nanostructures are analyzed using the conventional SIE approach and the TCM formalism. By comparing these results, the modes that are responsible of the observed scattering and absorption characteristics can be identified. These solutions can be further utilized in the design and tuning nanoantenna configurations for specific application purposes. [ABSTRACT FROM PUBLISHER]