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Class imbalance problems have received a lot of attention throughout the last few years. It poses considerable hurdles to conventional classifiers, especially when combined with overlapping instances, where the complexity of the classification task increases. In this study, we have proposed a novel density-based method that combines the Ordering Points To Identify the Clustering Structure (OPTICS) algorithm with the Naive-Bayes approach to effectively handle overlapped and imbalanced problems at the same time, known as OPTICS-based k-Naive Bayes (Ok-NB). The Ok-NB method is used to correctly identify and construct the training data into overlapping and non-overlapping groups based on their density and reachability, while the Naive-Bayes technique is used to correctly map the test data samples to the appropriate class for accurate output. It offers adaptability and reliability in classifying complex datasets with overlapping and imbalanced properties. Cluster-based proximity assessment and probabilistic classification are combined to improve classification accuracy and guarantee that the most reliable neighbours’ opinions are given the greatest weight during the decision-making process. Extensive experiments were conducted on 21 benchmark datasets and the experiment results demonstrate how effectively the suggested approach works to achieve high classification accuracy. This proves the effectiveness and superiority of this proposed approach compared to existing state-of-the-art methods in tackling overlapping and imbalance challenges in classification tasks.

In this article, a plasmonic gold nanoantenna is proposed as a sensor to monitor refractive index variations between 1.30 and 1.35. These values are defined since they are characteristic of, for instance, water-based solutions, DNA, or haemoglobin. To simulate the device a novel model is used, which takes advantage of the wave-particle dualism and the generalised Fresnel coefficients for absorbing media. Although it is a time-domain model, in this research work the model is improved to compute steady state and frequency-domain results. The response to a Dirac excitation is obtained using that novel model. The steady state is reached for a long pulse emission. The long pulse emission is emulated by a Dirac comb and consequently, the optical response of the device for this kind of excitation is obtained considering the sum of several Dirac's responses shifted in time. Then, steady state might be reached as suggested by the presented results. Taking into account the obtained pulse responses, the refractive index sensor for the range 1.30–1.35 is proposed. The obtained results suggest that 350 nm and 450 nm are the best wavelengths to detect these analyte variations. The sensitivity reaches values up to around 110%/RIU, but sensitivities around 80%/RIU are computed within the range 250–500 nm.

Given the recent advances in information technology, speed has become an important requirement in data transmission. In this regard and given that an LED (light emitting diode) can turn on and off for several thousands, even millions, of times per second, then LiFi (light fidelity) technology has strong advantages over WiFi (wireless fidelity) in terms of speed in data transmission. In this research project, a consortium of industrial and academic partners have decided to evaluate the maturity of LiFi technology by designing a demonstrator that showcases an efficient and speedy intra-vehicle data transmission system. The demonstrator implements a two-way LiFi communication between the reading light of a vehicle and a portable device, such as a tablet or smartphone. This nomadic device must display, via an interface, receiving transmitted data in real time. The data is of type RNT (Digital Terrestrial Radio) and TNT (Digital Terrestrial Television) provided by an in-house antenna. LiFi depends on optical technology hence, the devices’ optical characteristics have significant influences on the system. This paper presents various conducted experiments and techniques to improve the system’s throughput, communication range, and reception area. For instance, by replacing the reading light with one of better optical characteristics, the communication range and reception area improve. By using symmetrical power supply, the throughput improves. In the same manner, by using optical filters that eliminate noise, throughput likewise improves. We have indeed demonstrated that LiFi data transmission in the vehicle is feasible; low-definition videos were successfully transmitted. The paper also presents various possible techniques to still improve the system performance.

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 3-D imaging light detection and ranging (LiDAR) with a wide scanning angle of 147.5° $\times 11.6$ ° is shown. The LiDAR has the micro-electromechanical system (MEMS) scanner, which is the electromagnetic driving type produced by the silicon-on-insulator (SOI) process. The scanner has a large aperture size of 7 mm $\times $ 5 mm with the mechanical tilt angle of ±12.5° $\times $ ±3.4°. The rib structure of the MEMS mirror realizes the small distortion on the mirror surface in addition to the lightweight. The three laser diodes (LDs) are used to realize the wide scanning angle. The optics has the unique design and covers the three transmitting directions of the LDs with only one small photodetector that has a diameter of 0.5 mm. This single photodetector configuration contributes to the compactness in addition to low cost. The maximum measurable range of 40 m is demonstrated with the frame rate of 28 frames per second (fps) and $282\times 31$ pixels. [ABSTRACT FROM AUTHOR]

This paper explores how optical switching technologies can innovate future intra data center networks. The effectiveness of applying large-port-count optical switches is clarified by comparing the available scales and performances of electrical and optical switching networks. The two core technologies needed to make it happen are presented: large-port-count optical switches that have pay-as-you-grow scalability and a simple and fast switch control procedure. Different from the present multi-tier electrical switch network, single-tier large-port-count optical switches and their parallel configurations are shown to greatly simplify the network. Their combination offers low blocking rates and low latency even though the connection set-up is performed in a completely distributed and asynchronous manner where network wide synchronization and routing control are unneeded. The design and performance verification of our control network are detailed, and experiments on a control network emulation based on field programmable gate arrays are presented. The connection set-up latency of around 20 µs is verified within a floor (200 m) using our recently developed silicon photonic switch and tunable filter devices. The devices rely on the thermo-optic effect, but if we apply the electro-optic effect and adopt a simplified connection set-up procedure, the set-up latency is reduced to around 7 µs. The direction discussed here will pave the way for achieving bandwidth abundant and energy efficient data center networks in the future. [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]

Linear Discriminant Analysis (LDA) has been widely used in supervised dimensionality reduction fields. However, LDA is usually weak in tackling data with Non-Gaussian distribution due to its incapability of extracting the intrinsic structure of data. In order to learn the intrinsic information more effectively, some dimensionality reduction methods incorporate the adaptive full-connected graph into the algorithm frame, but the defect is that the calculation of each pairwise distance is very time-consuming. In this letter, we propose a novel fast adaptive local subspace learning with regressive regularization model to solve the supervised dimensional reduction problem. Firstly, the adaptive anchor point graph is used to capture local structure information, which can greatly reduce computation complexity. Secondly, by using regressive regularization, the samples from different classes can be better separated in the projected space and the workload of selecting the optimal reduced dimension is easier. Moreover, entropy regularization is used to derive more appropriate weights. Finally, extensive experiments are conducted on real world data sets to verify the superiority of our model. [ABSTRACT FROM AUTHOR]

We present a method of near-infrared image reconstruction based on spatial modulation instability in a photorefractive strontium barium niobate crystal. The conditions that lead to the formation of modulation instability at near-infrared are discussed depending on the theory of modulation instability gain. Experimental results of scattered image reconstruction at the 1064 nm wavelength show the maximum cross-correlation coefficient and cross-correlation gain are 0.57 and 2.09 respectively. This method is expected to be an aid for near-infrared imaging technologies. [ABSTRACT FROM AUTHOR]

The availability of novel materials is one of the bases of the development of science and technology. During the last decades, the research on artificial materials exhibiting novel electrical and magnetic properties received significant attention from the scientific and industrial communities. In particular, the so-called metamaterials represent an interdisciplinary field of investigation nowadays and offer promising applications in many fields, such as electromagnetism, optics, thermal, and acoustics. Metamaterials are engineered composite structures which can exhibit physical properties not readily observed in common materials available in nature. Their crucial aspect is to reproduce structured materials, whose repeated elementary cell represents the “metamolecule.” The linear dimensions of the cells are sub-wavelength. As a consequence, the material behaves uniformly. Special attention was received by metamaterials showing negative values of the effective permittivity and permeability in a given frequency range. In this paper, we revisit the concept of such macroscopic parameters, in particular, from the measurement point of view on a macroscopic scale. Indeed, an accurate characterization of such material properties is a key issue for paving new technological applications. Thus, we start from the very definition of the quantities of interest at a macroscopic level. We focus on the meaning of measurement of magnetism in composite magnetic materials, deriving the relevant measurement models. [ABSTRACT FROM AUTHOR]

We study the network locality improvements that can be achieved by using co-packaged optics in data center and high-performance computing (HPC) networks. The increased escape bandwidth offered by co-packaged optics can enable switches with speeds of 51.2 Tb/s and beyond. From a network architecture perspective, the key advantages of introducing co-packaged optics at the switch points include the implementation of large-scale topologies of 12,000 end points with 4× higher bisection bandwidth and the reduction of the required number of switches by >40% compared with state-of-the-art approaches. From a network operation perspective, improved network locality and faster operation can be achieved since the higher-radix switches can mitigate the impact of network contention. Placing applications under fewer leaf switches reduces the number of packets that cross the spine switches in a leaf-spine topology. The proposed scheme is evaluated via discrete-event simulations: we initially evaluate the network locality properties of the system by using virtual-machine traces from a production data center, and we subsequently quantify the performance improvements by simulating an all-to-all pattern for a variety of message sizes over a number of nodes. The results suggest that co-packaged optics form a promising solution for keeping up with bandwidth scaling in future networks. The virtual-machine analysis shows that large-scale applications can be placed under up to 50% fewer first-level switches, while the network analysis shows speedups of up to 7.1, which translates to execution time reductions of up to 26% and 42.7% for applications with communication ratios of 0.3 and 0.5, respectively. [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]

An optical approach for pigmented lesions detection in human skin is presented. As differences between normal skin tissue and pigmentation tissue (and even a change in pigmentation development) can be detected by their optical properties, this paper presents a new, potentially noninvasive approach for skin cancer detection. Since each wavelength has different penetration depth into the tissue and different absorption, the goal was to check whether a combination of information obtained from five different wavelengths, can increase the detection probability and reduce the false positive probability, compared to using only one wavelength. Temporal tracking of back-reflected secondary speckle patterns generated while illuminating the tested area with several lasers and applying periodic vibrations to the surface via a controlled vibration source at several stimulation frequencies. As a sequel to the previous work conducted in our laboratory which investigated pigmented lesions interaction with one light source, this work deals with increasing the number of parameters that are being looked at and considered at the same time. Using five wavelengths, 9 vibration frequencies and 19 signal analysis parameters, ex-vivo experiments were performed on porcine skin tissues and were analyzed using artificial intelligence tools which could detect the strong features for each wavelength individually. Combining the wavelengths produced impressive results compared to the results by each wavelength separately: both types of errors, false positive and false negative, decreased to less than 2%. Such a significant change in its impact on patients shows the value of this method. This paper shows the possibility of optically separating normal skin from pigmentation tissue, by using the advantages of multi-spectral optimization. This is a necessary proof of concept as a preliminary step toward our future experiments, which may differentiate between different types of pigmentation, and even malignancy and benign tissues.

Multi-channel structured light with orbital angular momentum (OAM) can be applied in different applications. For example, OAM modulation and OAM multiplexing in fiber optics communications, high-dimensional quantum cryptography-based OAM states for transmitting secure information across free-space, and independent data streams through OAM beams multiplexed free-space optical links. Using a simple and efficient system consisting of a spiral phase element (SPE) and a multi-channel vortex filter (MVF), we have converted input Gaussian beams into multi-channel OAM-based vortex beams for infrared wavelengths. An SPE has been designed, which generates optical vortices with wavelength-dependent topological charge (including fractional values). The resulting complex fields are optically relayed on a binary MVF designed by modulo- $2\pi $ phase addition of multiple fork gratings with topological charges 1, 2, and 3 and azimuthal orientations. In this way, the MVF generates beams with different OAM states for different carrier waves with different angles and maps them at desired locations in the detector plane. In this study, both $3\times 3$ , as well as a hexagonal configuration, were used. Furthermore, the experimentally obtained OAM spectrum qualitatively agrees with the results of numerical simulations, thus verifying our approach. The presented approach opens a new pathway for developing an efficient multi-channel OAM beams generator designed for a specific wavelength and illuminated by an input beam of different wavelengths over a broad spectral range.

To achieve a link budget capable of supporting high capacity free space optical communication (FSO), a high transmit power is required. However, the transmitter can become potentially hazardous to the human eye. For a C-band transmitter to be classified as Class 1 eye-safe, the transmit intensity should be limited such that the optical power passing through a 24.5 mm diameter area is below 10 dBm. In this work we used a 9-aperture transmit, single-aperture receive FSO system to reduce the transmit intensity. Wavelength division multiplexed (WDM) signals were divided into 9 groups and transmitted through 9 apertures as separate beams. The apertures were arranged in a 3 x 3 array at a 25 mm pitch, and the transmit power from each aperture was set to 10 dBm. As a validation of the system by numerical simulation of propagation over 220 m, we showed that the additional free space loss due to pointing errors for the beams transmitted through the off-center apertures was less than 7.4 dB, and that using multiple apertures can significantly increase the transmission capacity. In the outdoor demonstration we transmitted 35 WDM 400 Gb/s dual-polarization probabilistically shaped 16-ary quadrature amplitude modulation signals over 220 m. By distributing the WDM channels across the 9 apertures to suit the transmission loss from their positions in the 3 x 3 array, we demonstrated error-free real-time transmission of a record capacity of 14 Tb/s, while satisfying the requirements of the Class 1 laser safety standard. [ABSTRACT FROM AUTHOR]

Wedemonstrate a high-speed light fidelity (LiFi) communication system deploying ultra-high brightness laser-based white light illumination sources in a surface mount device (SMD) packaging platform. The LiFi transmitter SMD source provides 450 lumens of white light output with a brightness of 1000 cd/mm2 in a dual wavelength configuration comprising blue and infrared (IR) emitting laser diodes within the SMD. First, we present high-speed data transmission beyond 25 Gbit/s over a 3 meter channel distance with the combined data rates from the blue and IR lasers in the single SMD. Next, we present a 2.8 Gbit/s data rate with the dual wavelength laser SMD light source using a side-emissive fiber as the transmitter. This work proves the viability of LiFi systems deploying laser-based white light sources operating at very high data rates with the visible light and communication signal delivered in conventional free-space transmission architectures along with novel configurations using side-emitting fibers. [ABSTRACT FROM AUTHOR]

This article reports the development of an underwater imaging system and its trial on a moored surface buoy for in situ plankton monitoring of coastal waters. The imager features shadowless white light illumination by an orthogonal lamellar lighting design, resulting in high-quality underwater darkfield color imaging of planktonic particles in the size range of ∼200 μm to 40 mm and effective reduction of zooplankton phototaxis. Through raft and buoy trials, 46 804 plankton and suspending particle images have been annotated through a human–machine mutually assisted effort into a data set with 90 categories. In the meanwhile, a deep learning model based on a triclassification VGGNet-11 and multiclassification ResNet-18 convolutional neuron networks in a two-staged hierarchy has also been trained and developed. The model has been applied with human supervision to semiautomatically analyze a total of 1 545 187 images obtained from a buoy trial for six months from late spring to early winter of 2020. The high temporal resolution results well documented the variation of the mesoplankton community structure in two time series of 38 days in summer and 54 days in autumn of the target sea region. In addition, the dominant species in the trial period and a zooplankton outbreak that had threatened the safety of the nearby nuclear power plants were quantitatively analyzed. The system is expected to become a new entry into the toolkit for marine surface buoy platforms to upscale their capabilities for more comprehensive in situ plankton monitoring. [ABSTRACT FROM AUTHOR]

Thermal tunability for distributed feedback lasers is generally done at slow tuning speed. We study laser current boosting and implement a pre-equalization stage for short wavelength jump, improving the tuning time to the half. A wider jump is also done under a more practical context. [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]

Industry 4.0 (or 4th industrial revolution) facilitates horizontal and vertical digital information flow along value chains up to the end-customer and is highly relevant in a broad variety of industries. Augmented reality (AR) is a key technology in Industry 4.0, which connects the virtual and real-world environments using such digital information flows. In doing so, the technology relies upon the systems that includes hardware and software components. Particularly, optics and photonics are of much importance in the display and processing of information in these systems. However, a particular challenge is that the AR-based systems have not been adopted in the industry as much as other technologies even after several decades of their existence. Based on review of academic literature, an industrial survey and experiments conducted in the industry, this article aims to identify success factors and challenges of AR systems and metrics of photonic components that can form the basis of an AR* framework for photonics-based system design for future research. [ABSTRACT FROM AUTHOR]

As the reach of optical communications continues to shrink, photonics is moving from rack-to-rack datacom links to centimeter-scale in-computer applications (computercom) where different architectures are needed. Integrated optical microring resonators (MRRs) are emerging as an attractive choice for fulfilling the more stringent area and efficiency requirements: They offer scaling by wavelength division multiplexing (WDM) and high bandwidth densities. In this paper we present compact electro-optical transmit (TX) and receive (RX) macros for computercom monolithically integrated in 45 nm CMOS. They operate with MRR modulators and photodetectors and include all necessary electronics and optics to enable optical links between on-chip data sources and sinks. A most compact implementation for thermal stabilization was enabled by sensing the optical device's bias currents in the driving electronics instead of using external operating point sensing optics. Using a field-effect transistor as heating element — as is possible in monolithic integration platforms — further reduces area and power necessary for thermal control. The TX macro is shown to work for data rates up to 16 Gb/s with a 5.5 dB extinction ratio (ER) and 2.4 dB insertion loss (IL). The RX macro demonstrates a sensitivity of 71 µApp at 12 Gb/s for a BER ≤ 10−10. An intra-chip link built with the macros achieves ≤2.35 pJ/b electrical efficiency and a BER ≤10−10 at 10 Gb/s. Both macros are realized within 0.0073 mm2 which amounts to 1.4 Tb/s/mm2 bandwidth density per macro. [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]

We report an elliptical beam design for aberration mitigation in high-resolution optical coherence tomography (OCT). We polished a large angle on the fiber terminal facet in the sample arm to make a non-rotational symmetric beam with different numerical apertures (NA) for the two axes vertical to the optical axis. By sacrificing the resolution in the out-of-plane transverse direction, the elliptical beam mitigated the aberration introduced by the focusing optics in the OCT system. The elliptical beam with a doubled NA in the in-plane transverse direction promoted the axial field-of-view (FOV) by about 50% and increased the signal back-coupling efficiency by about 25%. We verified the feasibility of the design by imaging the USAF 1951 resolution chart, swine cornea ex vivo, and human skin in vivo. Results show that the proposed method relieves aberration-related problems in high-resolution OCT. [ABSTRACT FROM AUTHOR]

A rigorous theory for the synthesis of offset dual reflector antennas is presented. The synthesis problem is posed as a three dimensional vector field which becomes the surface normals to one of the reflectors. The ray trace which defines the vector field is calculated from the reflection law at one reflector and a constant path length requirement. Implicit in the definition of the vector field is the mapping from the input wavefront to the output wavefront. The Pfaffian integrability condition is applied to the vector field which leads to a partial differential equation (PDE) for the input to output mapping. Integrating this PDE coupled to the PDE for the shape of the first reflector yields the desired solution. The method allows for a wide choice of the input to output mapping and combined with a judicious choice of geometry produces practical designs which outperform traditional conic section designs. The use of an explicit existence theorem in the problem formulation is innovative and leads to simpler software which give excellent results. Unlike previous work, much of the algebra is done without reference to coordinate frames, simplifying the presentation and relegating algebraic details to symbolic software. A novel method for integrating the coupled PDE's is introduced.

Harmonic impedance estimation and suitable evaluation index selection are the key steps of harmonic contribution evaluation. Most of the traditional harmonic impedance estimation methods are only applicable to the scenario, where the background harmonic is stable and the utility impedance is constant. However, this scenario will change in many cases due to the fluctuation of harmonic, the change of system operation mode and so on. In order to improve the estimation accuracy for harmonic impedance, a harmonic impedance estimation method is proposed in this paper based on similarity measure and ordering points to identify the clustering structure (OPTICS). The total harmonic contribution index and harmonic comprehensive contribution index are proposed based on subjective analytic hierarchy process to simplify the evaluation results. Simulation analysis and their comparison with the traditional methods reveal that the proposed harmonic impedance estimation method can reduce the influence of background harmonic voltage fluctuation and utility impedance change, making the harmonic impedance estimation result more accurate. Besides, the proposed total harmonic contribution index and harmonic comprehensive contribution index can effectively simplify contribution evaluation results, which provide a new methodology for the evaluation of harmonic contribution.

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]

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]

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]

Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) shows great potential for forest height retrieval. However, there are abundant noise photons in the ICESat-2 data, which make the accurate extraction of global forest heights challenging. In this letter, a novel algorithm based on the clustering method of ordering points to identify the clustering structure (OPTICS) was proposed to remove noise photons. First, we modified the circular shape of the search area in the OPTICS algorithm to an elliptical shape. Second, a distance ordering of all photons was generated using the modified OPTICS algorithm. Finally, signal photons were effectively detected using distance thresholds set by the Otsu method. To evaluate the algorithm performance, both the simulated and real ICESat-2 data were applied to our proposed algorithm. In addition, we compared our algorithm with another noise removal algorithm based on the modified density-based spatial clustering of applications with noise (DBSCAN). The results show that our algorithm works well in distinguishing the signal and noise photons as indicated by high F values. Compared with the modified DBSCAN, our algorithm performs better in filtering out noise photons regardless of the simulated or real ICESat-2 data sets. In addition, the results also indicate that our algorithm is robust because it is insensitive to the clustering parameters. Overall, the new proposed algorithm is effective for removing noise photons in the ICESat-2 data. [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]

We propose a new thin and flat virtual reality (VR) display design using a Fresnel lenslet array, a Fresnel lens, and a polarization-based optical folding technique. The proposed optical system has a wide field of view (FOV) of 102°x102°, a wide eye-box of 8.8 mm, and an ergonomic eye-relief of 20 mm. Simultaneously, only 3.3 mm of physical distance is required between the display panel and the lens, so that the integrated VR display can have a compact form factor like sunglasses. Moreover, since all lenslet of the lenslet array is designed to operate under on-axis condition with low aberration, the discontinuous pupil swim distortion between the lenslets is hardly observed. In addition, all on-axis lenslets can be designed identically, reducing production cost, and even off-the-shelf Fresnel optics can be used. In this paper, we introduce how we design system parameters and analyze system performance. Finally, we demonstrate two prototypes and experimentally verify that the proposed VR display system has the expected performance while having a glasses-like form factor. [ABSTRACT FROM AUTHOR]

Optically transparent conductors (TCs) have been implemented and adopted into next-generation transmission lines and other RF structures from UHF to millimeter-wave (mmWave) applications. A current method of evaluating the performance of optically TCs uses a figure of merit (FOM) which is frequency agnostic. A new FOM for optically TCs at RF, microwave, and millimeter-wave frequencies is presented and provides distinction to the TC FOM proposed in 1976 where it adds a frequency dependence, by incorporating the skin effect requirement. A detailed analysis of the new FOM for both transparent conducting oxides and mesh conductors is presented and compared using TC literature data analyzed at 24 and 240 GHz where large FOM variation is shown. The manuscript shows the new RF FOM and classical FOM can vary by up to a factor of 10 when the skin depth of the conductor is not considered. [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]

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]

An optical approach for pigmented lesions detection in human skin is presented. As differences between normal skin tissue and pigmentation tissue (and even a change in pigmentation development) can be detected by their optical properties, this paper presents a new, potentially noninvasive approach for skin cancer detection. Since each wavelength has different penetration depth into the tissue and different absorption, the goal was to check whether a combination of information obtained from five different wavelengths, can increase the detection probability and reduce the false positive probability, compared to using only one wavelength. Temporal tracking of back-reflected secondary speckle patterns generated while illuminating the tested area with several lasers and applying periodic vibrations to the surface via a controlled vibration source at several stimulation frequencies. As a sequel to the previous work conducted in our laboratory which investigated pigmented lesions interaction with one light source, this work deals with increasing the number of parameters that are being looked at and considered at the same time. Using five wavelengths, 9 vibration frequencies and 19 signal analysis parameters, ex-vivo experiments were performed on porcine skin tissues and were analyzed using artificial intelligence tools which could detect the strong features for each wavelength individually. Combining the wavelengths produced impressive results compared to the results by each wavelength separately: both types of errors, false positive and false negative, decreased to less than 2%. Such a significant change in its impact on patients shows the value of this method. This paper shows the possibility of optically separating normal skin from pigmentation tissue, by using the advantages of multi-spectral optimization. This is a necessary proof of concept as a preliminary step toward our future experiments, which may differentiate between different types of pigmentation, and even malignancy and benign tissues. [ABSTRACT FROM AUTHOR]

Silica waveguides are often etched by reactive ion etch (RIE) processes. These processes can leave residual topography that can increase optical loss. We investigated the relation between optical loss and various RIE etch. A wet etch step meant to remove microstructures was also considered and compared. Ridge waveguides were fabricated in plasma enhanced chemical vapor deposited films by three different RIE processes, each with a different gas composition, pressure setting, and applied power setting. Half of each set of waveguides were also subjected to a hydrofluoric acid (HF) solution. The waveguides were tested for optical transmission via the cutback method. The transmission vs waveguide length measurements were plotted to fit an exponential curve and the optical loss and measurement uncertainty for each waveguide set was calculated. Clear distinctions in optical loss were found between the different RIE processes. The HF treatment also has an effect, significantly reducing optical loss for two processes and increasing it for the third. Of the tested RIE processes, one can be suggested for silica waveguides. It results in the lowest optical loss and coincidently has the fastest etch rate. [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]

Based on the theory of transformation optics (TO), a new and simple method for generating multimodal orbital angular momentum (OAM) carrying beams in 3-D space is proposed in this letter. The proposed 3-D arbitrary-way multimodal OAM generator only requires an electric dipole as the source. It consists of a four-way plane waves converter and four multimodal OAM generators. Since this method only requires the operation of radial scaling map, different topological charge modes can be easily obtained by appropriately setting the sizes of the physical geometries. [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]