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  • 1
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-03-31
    Description: Infrared photodetector based on lead sulfide (PbS) colloidal quantum dot has been shown to be a promising candidate for infrared detectors, due to the low-cost process of fabrication and their extremely high sensitivity. Moreover, these photodetectors have successfully achieved ultrahigh detectivity—exceeding the indium gallium arsenide-based photodetectors—at room temperature. In this paper, PbS colloidal quantum dots have been synthesized through an all-chemical solution process and their X-ray diffraction patterns have been analyzed to verify the quality of the product. Transmission electron micrograph microscopy image confirms the production of 10-nm PbS nanoparticles. The as-synthesized PbS colloidal quantum dots were mixed with MEH-PPV to form a hybrid nanocomposite. PbS/MEH-PPV hybrid nanocomposite was used as an active material to detect infrared photons and convert into electrical current. The photoconductive photodetector was fabricated by drop casting the hybrid nanocomposite on interdigitated electrodes and tested under different conditions. To study the effect of silver nanoparticles on the performance of the device, different concentrations of Ag/PbS composition were used in the structure of the photodetector. The results show that the Ag additive reduces dark current due to band bending and increases photocurrent through plasmonic effect. Thus, a photoconductive photodetector with improved photosensitivity and enhanced performance has been achieved.
    Print ISSN: 0018-9197
    Electronic ISSN: 1558-1713
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 2
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-03-31
    Description: Nano-groove arrays incorporated into a freestanding GaN membrane are proposed for coupling with visible light. The coupling of transverse electric mode light over the entire visible wavelength region into and out of the planar membrane is thoroughly investigated herein by performing a finite element method analysis. Coupling can be regulated by device parameters such as groove depth, membrane thickness, grating period, and duty cycle. Single-band coupling featuring tunable coupling bands can be realized, with the peak dual coupling efficiency reaching 0.55. This study paves the way for realizing planar photonics devices at specific single wavelengths. The proposed device is a suitable candidate for use in optical filters, de-multiplexers, planar photonic sensors, and other devices.
    Electronic ISSN: 1943-0655
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 3
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-03-31
    Description: Geiger-mode avalanche photodiode (Gm-APD) offers 3D imaging lidar much better capability in terms of detection sensitivity. However, a range walk error (RWE) exists in Gm-APDs which refers to the fluctuation of the measured distance as a function of the intensity of echo pulses. In this paper, we present a real-time restraint method for RWE implemented by unequally intensity-dividing the echo pulses into two Gm-APDs. The difference image of two depth images measured by the divided beams is a matrix of RWE distribution and the intensity image is used to censor the anomalous pixels in the matrix. Combined with the matrix of RWE distribution, an accurate depth image with low RWE can be obtained. Experimental results demonstrate that the proposed method reduces approximately 86% RWE of the conventional method in real time.
    Electronic ISSN: 1943-0655
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 4
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-03-31
    Description: Group-III nitride-based ultraviolet (UV) quantum-disks (Qdisks) nanowires (NWs) light-emitting diodes grown on silicon substrates offer a scalable, environment-friendly, compact, and low-cost solution for numerous applications in solid-state lighting, spectroscopy, and biomedical. However, the internal quantum efficiency, injection efficiency, and extraction efficiency need to be further improved. The focus of this paper encompasses investigations based on structural optimization, device simulation, and device reliability. To optimize a UV-A (320–400 nm) device structure, we utilize the self-assembled Qdisks NWs with varying Qdisks thickness to study carrier separation in active-region and implement an improved p-contact-layer to increase the output power. By simulation, we found a 100× improvement in the direct recombination rate for samples with thicker Qdisks thickness of ∼5 monolayers (MLs) compared to the sample with ∼2 MLs-thick Qdisks. Moreover, the sample with graded top Mg-doped AlGaN layer in conjunction with thin Mg-doped GaN layer shows 10× improvement in the output power compared to the samples with thicker top Mg-doped GaN absorbing contact layer.  A fitting with ABC model revealed the increase in nonradiative recombination centers in the active region after a soft stress test.  This paper aims to shed light on the research efforts required for furthering the UV NWs LED research for practical applications.
    Electronic ISSN: 1943-0655
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 5
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-03-31
    Description: We propose a variable mode excitation ratio method for measuring the attenuation coefficients of individual transmission modes in few-mode fiber (FMF). The experimental results we obtained with 2LP mode fiber agree well with those measured by the conventional mode-selective launching method and the optical time domain reflectometer (OTDR) method. We also show that the proposed method can be applied to an FMF with more than two mode groups by measuring the transmitted power property under various mode excitation ratios with a multiple mode group combination. Finally, we reveal that our method can provide an accurate modal attenuation coefficient even if we cannot use a mode multiplexer with a sufficient mode extinction ratio.
    Print ISSN: 0733-8724
    Electronic ISSN: 1558-2213
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  • 6
    Publication Date: 2018-01-03
    Description: Few-layer graphene/silicon quantum dots/silicon (FLG/SiQDs/Si) heterojunction solar cells consisting of a layer of SiQDs sandwiched between FLG and p- or n-type Si is examined by a device physics model incorporated with the optical characteristics of FLG and SiQDs. FLG/SiQDs/Si solar cells enhance short-circuit current density, because charge carriers can tunnel through the energy states in SiQDs. In addition, the quantum size effects result in a shift in the conduction and valence subband position of SiQDs, which leads to a wide band gap and consequently the improvement of open-circuit voltage for FLG/SiQDs/Si solar cells. In addition, further improvement in the performance of FLG/SiQDs/Si solar cells can be obtained by tuning the size of SiQDs and FLG properties.
    Print ISSN: 0018-9197
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  • 7
    Publication Date: 2018-01-03
    Description: Combining intracavity etalon (IE) locked on a laser oscillating mode with a deliberately introduced nonlinear loss, the tuning range of a continuous-wave (CW) single-frequency laser is significantly expanded to transcend the traditional limitation of a free spectral range (FSR) of IE. Due to the action of the nonlinear loss, the frequency of laser oscillating mode can be continuously and smoothly tuned without any mode-hopping in a tuning range much larger than FSR of IE. We theoretically analyze the physical mechanism behind the influence of nonlinear loss on the tuning range expansibility of the laser and experimentally demonstrated the effectiveness of the presented method. By means of this method, the ultrawide continuous frequency scanning range of 222.4 GHz at 532 nm is implemented. The theoretical analysis and the experimental results are in good agreement.
    Print ISSN: 1077-260X
    Electronic ISSN: 1558-4542
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 8
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Spectral and polarimetric contents of the light reflected from an object contain useful information on material type and surface characteristics of the object. Jointly exploiting spatial, spectral, and polarimetric information helps detect camouflage targets. Motivated by the vision mechanism of some known aquatic insects, we construct a bioinspired multiband polarimetric imaging system using a camera array, which simultaneously captures multiple images of different spectral bands and polarimetric angles. But the disparity between the fixed positions of each component camera leads to the loss of information in the boundary region and a reduction in the field of view (FOV). In order to overcome the limits, this paper presents a deep learning method for FOV expansion, incorporating the gradient prior of the image into a nine-dimensional convolutional neural network's framework to learn end-to-end mapping between the incomplete images and the FOV-expanded images. With FOV expansion, the proposed model recovers significant missing information. For the problem of insufficient training data, we construct the training dataset and propose the corresponding training methods to achieve good convergence of the network. We also provide some experimental results to validate its state-of-the-art performance of FOV expansion.
    Electronic ISSN: 1943-0655
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 9
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: A new tensor-based approach, which is capable of significantly increasing the degrees of freedom (DOF) of an L-shaped array consisting of two orthogonal uniform linear arrays (ULAs), is proposed. By dividing each ULA into some overlapping subarrays and then combining their received signals into a data tensor, a new cross-correlation tensor between the two data tensors from the two ULAs is built. Analyses show that such a cross-correlation tensor can be transformed into an equivalent received data matrix of a virtual uniform rectangular array (URA). Under the constraint of a fixed actual number of physical sensors, the optimal number of the subarrays is found by maximizing the DOF of the URA. It is shown that a virtual URA with approximately $0.34{{(M+1)}^{2}}$ DOF can be obtained from an L-shaped array with $2M$ physical sensors. To exploit the increased DOF for the two dimensional (2-D) DOA estimation without the multidimensional search, a parallel factor (PARAFAC) model of the URA is provided so that the PARAFAC decomposition can be utilized to do the 2-D DOA estimation effectively. Simulation results demonstrate that the proposed method can yield a better estimation performance and resolve more sources than some computationally efficient methods reported in literature.
    Print ISSN: 1070-9908
    Electronic ISSN: 1558-2361
    Topics: Electrical Engineering, Measurement and Control Technology
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  • 10
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: In this letter, we consider the inter-relay interference (IRI) problem for amplify-and-forward (AF) two-path successive relay networks. To reduce processing burden for IRI cancelation at the relay nodes, a novel precoding-based interference cancelation scheme based on row-space mapping is proposed, where a pair of orthogonal precoding matrices is alternately utilized to project the source data onto the null space of the received data that is independent of channel state information (CSI). By designing a combined decoding and re-encoding scheme, both the IRI signal and accumulated noise are perfectly suppressed at the relay nodes. Simulation results show that the proposed scheme is significantly better than the channel estimate based interference cancelation schemes.
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  • 11
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Print ISSN: 0278-0062
    Electronic ISSN: 1558-254X
    Topics: Medicine , Technology
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  • 12
    Publication Date: 2018-01-03
    Description: This letter introduces a method based on the Hilbert–Huang transform (HHT) to estimate the fundamental frequency of nonstationary noisy speech signals. For this purpose, the target signals are analyzed by means of the ensemble empirical mode decomposition and the Hilbert transform. The main contribution of the proposed solution, namely HHT-Amp, relies on the extraction of pitch information from the instantaneous amplitude of the first decomposition modes. The HHT-Amp and four competitive algorithms are evaluated considering speech signals corrupted by five acoustic noises with different nonstationarity degrees. The HHT-Amp achieves the lowest gross error rate and mean absolute error for the most severe noisy conditions. This demonstrates that the proposed approach outperforms the baseline methods in estimating the fundamental frequency of noisy speech.
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  • 13
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: This paper describes a new image reconstruction method for digital breast tomosynthesis (DBT). The new method incorporates detector blur into the forward model. The detector blur in DBT causes correlation in the measurement noise. By making a few approximations that are reasonable for breast imaging, we formulated a regularized quadratic optimization problem with a data-fit term that incorporates models for detector blur and correlated noise (DBCN). We derived a computationally efficient separable quadratic surrogate (SQS) algorithm to solve the optimization problem that has a non-diagonal noise covariance matrix. We evaluated the SQS-DBCN method by reconstructing DBT scans of breast phantoms and human subjects. The contrast-to-noise ratio and sharpness of microcalcifications were analyzed and compared with those by the simultaneous algebraic reconstruction technique. The quality of soft tissue lesions and parenchymal patterns was examined. The results demonstrate the potential to improve the image quality of reconstructed DBT images by incorporating the system physics model. This paper is a first step toward model-based iterative reconstruction for DBT.
    Print ISSN: 0278-0062
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  • 14
    Publication Date: 2018-01-03
    Description: Histotripsy utilizes focused ultrasound to generate bubble clouds for transcutaneous tissue liquefaction. Bubble activity maps are under development to provide image guidance and monitor treatment progress. The aim of this paper was to investigate the feasibility of using plane wave B-mode and passive cavitation images to be used as binary classifiers of histotripsy-induced liquefaction. Prostate tissue phantoms were exposed to histotripsy pulses over a range of pulse durations (5– $20~mu text{s}$ ) and peak negative pressures (12–23 MPa). Acoustic emissions were recorded during the insonation and beamformed to form passive cavitation images. Plane wave B-mode images were acquired following the insonation to detect the hyperechoic bubble cloud. Phantom samples were sectioned and stained to delineate the liquefaction zone. Correlation between passive cavitation and plane wave B-mode images and the liquefaction zone was assessed using receiver operating characteristic (ROC) curve analysis. Liquefaction of the phantom was observed for all the insonation conditions. The area under the ROC (0.94 versus 0.82), accuracy (0.90 versus 0.83), and sensitivity (0.81 versus 0.49) was greater for passive cavitation images relative to B-mode images ( ${p} 〈 0.05$ ) along the azimuth of the liquefaction zone. The specificity was greater than 0.9 for both imaging modalities. These results demonstrate a stronger correlation between histotripsy-induced liquefaction and passive cavitation imaging compared with the plane wave B-mode imaging, albeit with limited passive cavitation image range resolution.
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  • 15
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Similarity measure is a main core of image registration algorithms. Spatially varying intensity distortion is an important challenge, which affects the performance of similarity measures. Correlation among the pixels is the main characteristic of this distortion. Similarity measures such as sum-of-squared-differences (SSD) and mutual information ignore this correlation; hence, perfect registration cannot be achieved in the presence of this distortion. In this paper, we model this correlation with the aid of the low rank matrix theory. Based on this model, we compensate this distortion analytically and introduce rank-regularized SSD (RRSSD). This new similarity measure is a modified SSD based on singular values of difference image in mono-modal imaging. In fact, image registration and distortion correction are performed simultaneously in the proposed model. Based on our experiments, the RRSSD similarity measure achieves clinically acceptable registration results, and outperforms other state-of-the-art similarity measures, such as the well-known method of residual complexity.
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  • 16
    Publication Date: 2018-01-03
    Description: The analysis of the pure motion of subnuclear structures without influence of the cell nucleus motion and deformation is essential in live cell imaging. In this paper, we propose a 2-D contour-based image registration approach for compensation of nucleus motion and deformation in fluorescence microscopy time-lapse sequences. The proposed approach extends our previous approach, which uses a static elasticity model to register cell images. Compared with that scheme, the new approach employs a dynamic elasticity model for the forward simulation of nucleus motion and deformation based on the motion of its contours. The contour matching process is embedded as a constraint into the system of equations describing the elastic behavior of the nucleus. This results in better performance in terms of the registration accuracy. Our approach was successfully applied to real live cell microscopy image sequences of different types of cells including image data that was specifically designed and acquired for evaluation of cell image registration methods. An experimental comparison with the existing contour-based registration methods and an intensity-based registration method has been performed. We also studied the dependence of the results on the choice of method parameters.
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  • 17
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: We present a comparative study for discriminative anatomy detection in high dimensional neuroimaging data. While most studies solve this problem using mass univariate approaches, recent works show better accuracy and variable selection using a sparse classification model. Two types of image-based regularization methods have been proposed in the literature based on either a Graph Net (GN) model or a total variation (TV) model. These studies showed increased classification accuracy and interpretability of results when using image-based regularization, but did not look at the accuracy and quality of the recovered significant regions. In this paper, we theoretically prove bounds on the recovered sparse coefficients and the corresponding selected image regions in four models (two based on GN penalty and two based on TV penalty). Practically, we confirm the theoretical findings by measuring the accuracy of selected regions compared with ground truth on simulated data. We also evaluate the stability of recovered regions over cross-validation folds using real MRI data. Our findings show that the TV penalty is superior to the GN model. In addition, we showed that adding an l 2 penalty improves the accuracy of estimated coefficients and selected significant regions for the both types of models.
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  • 18
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: We present a direct (noniterative) algorithm for 1-D quadratic data fitting with neighboring intensity differences penalized by the Huber function. Applications of such an algorithm include 1-D processing of medical signals, such as smoothing of tissue time concentration curves in kinetic data analysis or sinogram preprocessing, and using it as a subproblem solver for 2-D or 3-D image restoration and reconstruction. dynamic programming was used to develop the direct algorithm. The problem was reformulated as a sequence of univariate optimization problems, for ${k} =textsf {1}, ldots , {N}$ , where ${N}$ is the number of data points. The solution to the univariate problem at index ${k}$ is parameterized by the solution at ${k}+textsf {1}$ , except at ${k}={N}$ . Solving the univariate optimization problem at ${k}={N}$ yields the solution to each problem in the sequence using back-tracking. Computational issues and memory cost are discussed in detail. Two numerical studies, tissue concentration curve smoothing and sinogram preprocessing for image reconstruction, are used to validate the direct algorithm and illustrate its practical applications. In the example of 1-D curve smoothing, the efficiency of the direct algorithm is compared with four iterative methods: the iterative coordinate descent, Nesterov’s accelerated gradient descent algorithm, FISTA, and an off-the-shelf second order method. The first two methods were applied to the primal problem, the others to the dual problem. The comparisons show that the direct - lgorithm outperforms all other methods by a significant factor, which rapidly grows with the curvature of the Huber function. The second example, sinogram preprocessing, showed that robustness and speed of the direct algorithm are maintained over a wide range of signal variations, and that noise and streaking artifacts could be reduced with almost no increase in computation time. We also outline how the proposed 1-D solver can be used for imaging applications.
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  • 19
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: In diffusion MRI (dMRI), a good sampling scheme is important for efficient acquisition and robust reconstruction. Diffusion weighted signal is normally acquired on single or multiple shells in q-space. Signal samples are typically distributed uniformly on different shells to make them invariant to the orientation of structures within tissue, or the laboratory coordinate frame. The electrostatic energy minimization (EEM) method, originally proposed for single shell sampling scheme in dMRI, was recently generalized to multi-shell schemes, called generalized EEM (GEEM). GEEM has been successfully used in the human connectome project. However, EEM does not directly address the goal of optimal sampling, i.e., achieving large angular separation between sampling points. In this paper, we propose a more natural formulation, called spherical code (SC), to directly maximize the minimal angle between different samples in single or multiple shells. We consider not only continuous problems to design single or multiple shell sampling schemes, but also discrete problems to uniformly extract sub-sampled schemes from an existing single or multiple shell scheme, and to order samples in an existing scheme. We propose five algorithms to solve the above problems, including an incremental SC (ISC), a sophisticated greedy algorithm called iterative maximum overlap construction (IMOC), an 1-Opt greedy method, a mixed integer linear programming method, and a constrained non-linear optimization method. To our knowledge, this is the first work to use the SC formulation for single or multiple shell sampling schemes in dMRI. Experimental results indicate that SC methods obtain larger angular separation and better rotational invariance than the state-of-the-art EEM and GEEM. The related codes and a tutorial have been released in DMRITool. 1 1 https://diffusionmritool.github.io/tutorial_q- pacesampling.html
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  • 20
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: We present a novel method to segment instances of glandular structures from colon histopathology images. We use a structure learning approach which represents local spatial configurations of class labels, capturing structural information normally ignored by sliding-window methods. This allows us to reveal different spatial structures of pixel labels (e.g., locations between adjacent glands, or far from glands), and to identify correctly neighboring glandular structures as separate instances. Exemplars of label structures are obtained via clustering and used to train support vector machine classifiers. The label structures predicted are then combined and post-processed to obtain segmentation maps. We combine hand-crafted, multi-scale image features with features computed by a deep convolutional network trained to map images to segmentation maps. We evaluate the proposed method on the public domain GlaS data set, which allows extensive comparisons with recent, alternative methods. Using the GlaS contest protocol, our method achieves the overall best performance.
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  • 21
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Ultrasound molecular imaging (USMI) is accomplished by detecting microbubble (MB) contrast agents that have bound to specific biomarkers, and can be used for a variety of imaging applications, such as the early detection of cancer. USMI has been widely utilized in preclinical imaging in mice; however, USMI in humans can be challenging because of the low concentration of bound MBs and the signal degradation caused by the presence of heterogenous soft tissue between the transducer and the lesion. Short-lag spatial coherence (SLSC) beamforming has been proposed as a robust technique that is less affected by poor signal quality than standard delay-and-sum (DAS) beamforming. In this paper, USMI performance was assessed using contrast-enhanced ultrasound imaging combined with DAS (conventional CEUS) and with SLSC (SLSC-CEUS). Each method was characterized by flow channel phantom experiments. In a USMI-mimicking phantom, SLSC-CEUS was found to be more robust to high levels of additive thermal noise than DAS, with a 6dB SNR improvement when the thermal noise level was +6dB or higher. However, SLSC-CEUS was also found to be insensitive to increases in MB concentration, making it a poor choice for perfusion imaging. USMI performance was also measured in vivo using VEGFR2-targeted MBs in mice with subcutaneous human hepatocellular carcinoma tumors, with clinical imaging conditions mimicked using a porcine tissue layer between the tumor and the transducer. SLSC-CEUS improved the SNR in each of ten tumors by an average of 41%, corresponding to 3.0dB SNR. These results indicate that the SLSC beamformer is well-suited for USMI applications because of its high sensitivity and robust properties under challenging imaging conditions.
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  • 22
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: This paper presents a method for automatically calibrating and assessing the calibration quality of an externally tracked 2-D ultrasound (US) probe by scanning arbitrary, natural tissues, as opposed a specialized calibration phantom as is the typical practice. A generative topic model quantifies the posterior probability of calibration parameters conditioned on local 2-D image features arising from a generic underlying substrate. Auto-calibration is achieved by identifying the maximum a-posteriori image-to-probe transform, and calibration quality is assessed online in terms of the posterior probability of the current image-to-probe transform. Both are closely linked to the 3-D point reconstruction error (PRE) in aligning feature observations arising from the same underlying physical structure in different US images. The method is of practical importance in that it operates simply by scanning arbitrary textured echogenic structures, e.g., in-vivo tissues in the context of the US-guided procedures, without requiring specialized calibration procedures or equipment. Observed data take the form of local scale-invariant features that can be extracted and fit to the model in near real-time. Experiments demonstrate the method on a public data set of in vivo human brain scans of 14 unique subjects acquired in the context of neurosurgery. Online calibration assessment can be performed at approximately 3 Hz for the US images of $640times 480$ pixels. Auto-calibration achieves an internal mean PRE of 1.2 mm and a discrepancy of [2 mm, 6 mm] in comparison to the calibration via a standard phantom-based method.
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  • 23
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: The motion of the common carotid artery (CCA) wall has been established to be useful in early diagnosis of atherosclerotic disease. However, tracking the CCA wall motion from ultrasound images remains a challenging task. In this paper, a nonlinear state-space approach has been developed to track CCA wall motion from ultrasound sequences. In this approach, a nonlinear state-space equation with a time-variant control signal was constructed from a mathematical model of the dynamics of the CCA wall. Then, the unscented Kalman filter (UKF) was adopted to solve the nonlinear state transfer function in order to evolve the state of the target tissue, which involves estimation of the motion trajectory of the CCA wall from noisy ultrasound images. The performance of this approach has been validated on 30 simulated ultrasound sequences and a real ultrasound dataset of 103 subjects by comparing the motion tracking results obtained in this study to those of three state-of-the-art methods and of the manual tracing method performed by two experienced ultrasound physicians. The experimental results demonstrated that the proposed approach is highly correlated with (intra-class correlation coefficient ≥ 0.9948 for the longitudinal motion and ≥ 0.9966 for the radial motion) and well agrees (the 95% confidence interval width is 0.8871 mm for the longitudinal motion and 0.4159 mm for the radial motion) with the manual tracing method on real data and also exhibits high accuracy on simulated data (0.1161 ~ 0.1260 mm). These results appear to demonstrate the effectiveness of the proposed approach for motion tracking of the CCA wall.
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  • 24
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Recently, matrix gradient coils (also termed multi-coils or multi-coil arrays) were introduced for imaging and B 0 shimming with 24, 48, and even 84 coil elements. However, in imaging applications, providing one amplifier per coil element is not always feasible due to high cost and technical complexity. In this simulation study, we show that an 84-channel matrix gradient coil (head insert for brain imaging) is able to create a wide variety of field shapes even if the number of amplifiers is reduced. An optimization algorithm was implemented that obtains groups of coil elements, such that a desired target field can be created by driving each group with an amplifier. This limits the number of amplifiers to the number of coil element groups. Simulated annealing is used due to the NP-hard combinatorial nature of the given problem. A spherical harmonic basis set up to the full third order within a sphere of 20-cm diameter in the center of the coil was investigated as target fields. We show that the median normalized least squares error for all target fields is below approximately 5% for 12 or more amplifiers. At the same time, the dissipated power stays within reasonable limits. With a relatively small set of amplifiers, switches can be used to sequentially generate spherical harmonics up to third order. The costs associated with a matrix gradient coil can be lowered, which increases the practical utility of matrix gradient coils.
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  • 25
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: The use of appearance and shape priors in image segmentation is known to improve accuracy; however, existing techniques have several drawbacks. For instance, most active shape and appearance models require landmark points and assume unimodal shape and appearance distributions, and the level set representation does not support construction of local priors. In this paper, we present novel appearance and shape models for image segmentation based on a differentiable implicit parametric shape representation called a disjunctive normal shape model (DNSM). The DNSM is formed by the disjunction of polytopes, which themselves are formed by the conjunctions of half-spaces. The DNSM’s parametric nature allows the use of powerful local prior statistics, and its implicit nature removes the need to use landmarks and easily handles topological changes. In a Bayesian inference framework, we model arbitrary shape and appearance distributions using nonparametric density estimations, at any local scale. The proposed local shape prior results in accurate segmentation even when very few training shapes are available, because the method generates a rich set of shape variations by locally combining training samples. We demonstrate the performance of the framework by applying it to both 2-D and 3-D data sets with emphasis on biomedical image segmentation applications.
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  • 26
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Phase retrieval is an important tool for image recovery techniques based on Fourier spectrum. Different iterative algorithms have been developed to retrieve phase information. However, due to the nonconvex feature of the phase optimization problem, it remains a challenge to globally obtain the optimal phase information. In this work, we proposed an iterative algorithm to retrieve the global optimal phase information by adopting particle swarm optimization technique to the hybrid input–output scheme. By escaping the local minima using stochastic perturbations and information exchange among particles’ local solutions, the proposed scheme increases the possibility of reaching the global minimum in phase retrieval optimization. In the numerical simulations, the images reconstructed by the proposed scheme have an averaged mean-square error of 0.0055, which is, respectively, 43.88% and 36.78% smaller than those of the images reconstructed by hybrid input–output and guided hybrid input–output schemes. The feasibility of the proposed scheme was demonstrated by the results from actual experiments, which showed an agreement with the simulation. The proposed scheme is statistically capable of obtaining accurate phase information, and, therefore, can be applied to Fourier spectrum based image recovery techniques.
    Electronic ISSN: 1943-0655
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
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  • 27
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Massive multiple-input multiple-output (MIMO) has shown its great capabilities in improving spectral efficiency and energy efficiency, yet the high complexity and cost of hardware are huge challenges. In massive MIMO, antenna selection (AS) is still an effective way to decrease the number of radio frequency chains. In this letter, the AS problem in massive MIMO systems is studied with the consideration of maximizing the channel capacity. To eliminate the limitation of the traditional square maximum-volume (SMV) AS method, the theory of rectangular maximum-volume (RMV) submatrices is introduced. An AS algorithm based on RMV method is also developed for massive MIMO, which can be regarded as a postprocessing of the results of SMV method. Based on the result obtained from SMV method, the proposed algorithm can select a rectangular submatrix with maximum-volume from the channel matrix. Finally, the numerical simulations are presented to show the validity of the proposed RMV method.
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  • 28
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: We study the degrees of freedom (DoFs) of a multiple-input multiple-output $K$ -pair two-way relay channel with delayed channel state information (CSI) with $J$ distributed relays. In the considered model, we assume that the users are equipped with $M$ antennas and the relay with $N$ antennas. We propose two schemes, where the signaling design can be carried out either in each individual time slot or across multiple time slots with and without knowledge of CSI. The scheme involves a joint design of user beamforming matrices, relay beamforming matrices, and user postprocessing matrices, so as to meet interference neutralization and rank conditions. We show that the optimal DoF of $frac{N}{2K}$ per user can be reached for $frac{M}{N}geq 1$ for an arbitrary number of user pairs when $J=1$ . This implies that delayed CSI does not compromise the DoF performance of the considered model when $frac{M}{N}geq 1$ .
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  • 29
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Print ISSN: 0278-0062
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  • 30
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: We present a novel approach for improving the shape statistics of medical image objects by generating correspondence of skeletal points. Each object’s interior is modeled by an s-rep, i.e., by a sampled, folded, two-sided skeletal sheet with spoke vectors proceeding from the skeletal sheet to the boundary. The skeleton is divided into three parts: the up side, the down side, and the fold curve. The spokes on each part are treated separately and, using spoke interpolation, are shifted along that skeleton in each training sample so as to tighten the probability distribution on those spokes’ geometric properties while sampling the object interior regularly. As with the surface/boundary-based correspondence method of Cates et al. , entropy is used to measure both the probability distribution tightness and the sampling regularity, here of the spokes’ geometric properties. Evaluation on synthetic and real world lateral ventricle and hippocampus data sets demonstrate improvement in the performance of statistics using the resulting probability distributions. This improvement is greater than that achieved by an entropy-based correspondence method on the boundary points.
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  • 31
    Publication Date: 2018-01-03
    Description: Diffusion-weighted magnetic resonance imaging (DWI) is a key non-invasive imaging technique for cancer diagnosis and tumor treatment assessment, reflecting Brownian movement of water molecules in tissues. Since densely packed cells restrict molecule mobility, tumor tissues produce usually higher signal (a.k.a. less attenuated signal) on isotropic maps compared with normal tissues. However, no general quantitative relation between DWI data and the cell density has been established. In order to link low-resolution clinical cross-sectional data with high-resolution histological information, we developed an image processing and analysis chain, which was used to study the correlation between the diffusion coefficient (D value) estimated from DWI and tumor cellularity from serial histological slides of a resected non-small cell lung cancer tumor. Color deconvolution followed by cell nuclei segmentation was performed on digitized histological images to determine local and cell-type specific 2d (two-dimensional) densities. From these, the 3d cell density was inferred by a model-based sampling technique, which is necessary for the calculation of local and global 3d tumor cell count. Next, DWI sequence information was overlaid with high-resolution CT data and the resected histology using prominent anatomical hallmarks for co-registration of histology tissue blocks and non-invasive imaging modalities’ data. The integration of cell numbers information and DWI data derived from different tumor areas revealed a clear negative correlation between cell density and D value. Importantly, spatial tumor cell density can be calculated based on DWI data. In summary, our results demonstrate that tumor cell count and heterogeneity can be predicted from DWI data, which may open new opportunities for personalized diagnosis and therapy optimization.
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  • 32
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: In this paper, we propose a generalized joint sparsity regularization prior and reconstruction framework for the synergistic reconstruction of positron emission tomography (PET) and under sampled sensitivity encoded magnetic resonance imaging data with the aim of improving image quality beyond that obtained through conventional independent reconstructions. The proposed prior improves upon the joint total variation (TV) using a non-convex potential function that assigns a relatively lower penalty for the PET and MR gradients, whose magnitudes are jointly large, thus permitting the preservation and formation of common boundaries irrespective of their relative orientation. The alternating direction method of multipliers (ADMM) optimization framework was exploited for the joint PET-MR image reconstruction. In this framework, the joint maximum a posteriori objective function was effectively optimized by alternating between well-established regularized PET and MR image reconstructions. Moreover, the dependency of the joint prior on the PET and MR signal intensities was addressed by a novel alternating scaling of the distribution of the gradient vectors. The proposed prior was compared with the separate TV and joint TV regularization methods using extensive simulation and real clinical data. In addition, the proposed joint prior was compared with the recently proposed linear parallel level sets (PLSs) method using a benchmark simulation data set. Our simulation and clinical data results demonstrated the improved quality of the synergistically reconstructed PET-MR images compared with the unregularized and conventional separately regularized methods. It was also found that the proposed prior can outperform both the joint TV and linear PLS regularization methods in assisting edge preservation and recovery of details, which are otherwise impaired by noise and aliasing artifacts. In conclusion, the proposed joint sparsity regularization within the presented a- ADMM reconstruction framework is a promising technique, nonetheless our clinical results showed that the clinical applicability of joint reconstruction might be limited in current PET-MR scanners, mainly due to the lower resolution of PET images.
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  • 33
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Geometric distortion induced by the main B0 field disrupts the consistency of fetal echo planar imaging (EPI) data, on which diffusion and functional magnetic resonance imaging is based. In this paper, we present a novel data-driven method for simultaneous motion and distortion correction of fetal EPI. A motion-corrected and reconstructed T2 weighted single shot fast spin echo (ssFSE) volume is used as a model of undistorted fetal brain anatomy. Our algorithm interleaves two registration steps: estimation of fetal motion parameters by aligning EPI slices to the model; and deformable registration of EPI slices to slices simulated from the undistorted model to estimate the distortion field. The deformable registration is regularized by a physically inspired Laplacian constraint, to model distortion induced by a source-free background B0 field. Our experiments show that distortion correction significantly improves consistency of reconstructed EPI volumes with ssFSE volumes. In addition, the estimated distortion fields are consistent with fields calculated from acquired field maps, and the Laplacian constraint is essential for estimation of plausible distortion fields. The EPI volumes reconstructed from different scans of the same subject were more consistent when the proposed method was used in comparison with EPI volumes reconstructed from data distortion corrected using a separately acquired B0 field map.
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  • 34
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: In X-ray fluoroscopy, static overlays are used to visualize soft tissue. We propose a system for cardiac and respiratory motion compensation of these overlays. It consists of a 3-D motion model created from real-time magnetic resonance (MR) imaging. Multiple sagittal slices are acquired and retrospectively stacked to consistent 3-D volumes. Slice stacking considers cardiac information derived from the ECG and respiratory information extracted from the images. Additionally, temporal smoothness of the stacking is enhanced. Motion is estimated from the MR volumes using deformable 3-D/3-D registration. The motion model itself is a linear direct correspondence model using the same surrogate signals as slice stacking. In X-ray fluoroscopy, only the surrogate signals need to be extracted to apply the motion model and animate the overlay in real time. For evaluation, points are manually annotated in oblique MR slices and in contrast-enhanced X-ray images. The 2-D Euclidean distance of these points is reduced from 3.85 to 2.75 mm in MR and from 3.0 to 1.8 mm in X-ray compared with the static baseline. Furthermore, the motion-compensated overlays are shown qualitatively as images and videos.
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  • 35
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Magnetic particle imaging (MPI) is a promising new tomographic imaging method to detect the spatial distribution of superparamagnetic iron-oxide nanoparticles (SPIOs). The aim of this paper was to investigate the potential of MPI to quantify artificial stenoses in vessel phantoms. Custom-made stenosis phantoms (length 40 mm; inner diameter 8 mm) with different degrees of stenosis (0%, 25%, 50%, 75%, and 100%) were scanned in a custom-built MPI scanner (in-plane resolution: ~1–1.5 mm and field of view: 65 $times $ 29 $times $ 29 mm 3 ). Phantoms were filled with diluted Feru-carbotran [SPIO agent, 5 mmol (Fe)/l]. Each measurement (overall acquisition time: 20 ms per image, 400 averages) was repeated ten times to assess reproducibility. The MPI signal was used for semi-automatic stenosis quantification. Two stenosis evaluation approaches were compared based on the signal intensity profile alongside the stenosis phantoms. Using a novel multi-step image evaluation approach, MPI allowed for accurate quantification of different stenosis grades. While low grade stenoses were slightly over-estimated, high grade stenoses were slightly underestimated. In particular, the 0%, 25%, and 50% stenosis phantoms revealed a 6.2% ± 0.8, 25.7% ± 1.0, and 48.0% ± 1.5 stenosis, respectively. The higher grade 75% stenosis phantom revealed a 73.3% ± 2.8 and the 100% stenosis phantom a 95.8%± 1.9 stenosis. MPI accu- ately visualized and quantified different stenosis grades in vessel phantoms with high reproducibility demonstrating its great potential for fast and radiation-free preclinical cardiovascular imaging.
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  • 36
    Publication Date: 2018-01-03
    Description: By acquiring tomographic measurements with several distinct photon energy spectra, spectral computed tomography (spectral CT) is able to provide additional material-specific information compared with conventional CT. This information enables the generation of material selective images, which have found various applications in medical imaging. However, material decomposition typically leads to noise amplification and a degradation of the signal-to-noise ratio. This is still a fundamental problem of spectral CT, especially for low-dose medical applications. Inspired by the success for low-dose conventional CT, several statistical iterative reconstruction algorithms for spectral CT have been developed. These algorithms typically rely on detailed knowledge about the spectrum and the detector response. Obtaining this knowledge is often difficult in practice, especially if photon counting detectors are used to acquire the energy specific information. In this paper, a new algorithm for joint statistical iterative material image reconstruction is presented. It relies on a semi-empirical forward model which is tuned by calibration measurements. This strategy allows to model spatially varying properties of the imaging system without requiring detailed prior knowledge of the system parameters. We employ an efficient optimization algorithm based on separable surrogate functions to accelerate convergence and reduce the reconstruction time. Numerical as well as real experiments show that our new algorithm leads to reduced statistical bias and improved image quality compared with projection-based material decomposition followed by analytical or iterative image reconstruction.
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  • 37
    Publication Date: 2018-01-03
    Description: By exploiting cross-information among multiple imaging data, multimodal fusion has often been used to better understand brain diseases. However, most current fusion approaches are blind, without adopting any prior information. There is increasing interest to uncover the neurocognitive mapping of specific clinical measurements on enriched brain imaging data; hence, a supervised, goal-directed model that employs prior information as a reference to guide multimodal data fusion is much needed and becomes a natural option. Here, we proposed a fusion with reference model called “multi-site canonical correlation analysis with reference + joint-independent component analysis” (MCCAR+jICA), which can precisely identify co-varying multimodal imaging patterns closely related to the reference, such as cognitive scores. In a three-way fusion simulation, the proposed method was compared with its alternatives on multiple facets; MCCAR+jICA outperforms others with higher estimation precision and high accuracy on identifying a target component with the right correspondence. In human imaging data, working memory performance was utilized as a reference to investigate the co-varying working memory-associated brain patterns among three modalities and how they are impaired in schizophrenia. Two independent cohorts (294 and 83 subjects respectively) were used. Similar brain maps were identified between the two cohorts along with substantial overlaps in the central executive network in fMRI, salience network in sMRI, and major white matter tracts in dMRI. These regions have been linked with working memory deficits in schizophrenia in multiple reports and MCCAR+jICA further verified them in a repeatable, joint manner, demonstrating the ability of the proposed method to identify potential neuromarkers for mental disorders.
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  • 38
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-03
    Description: Accurate identification of the needle target is crucial for effective epidural anesthesia. Currently, epidural needle placement is administered by a manual technique, relying on the sense of feel, which has a significant failure rate. Moreover, misleading the needle may lead to inadequate anesthesia, post dural puncture headaches, and other potential complications. Ultrasound offers guidance to the physician for identification of the needle target, but accurate interpretation and localization remain challenges. A hybrid machine learning system is proposed to automatically localize the needle target for epidural needle placement in ultrasound images of the spine. In particular, a deep network architecture along with a feature augmentation technique is proposed for automatic identification of the anatomical landmarks of the epidural space in ultrasound images. Experimental results of the target localization on planes of 3-D as well as 2-D images have been compared against an expert sonographer. When compared with the expert annotations, the average lateral and vertical errors on the planes of 3-D test data were 1 and 0.4 mm, respectively. On 2-D test data set, an average lateral error of 1.7 mm and vertical error of 0.8 mm were acquired.
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  • 39
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-06
    Print ISSN: 1540-7977
    Electronic ISSN: 1558-4216
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  • 40
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: The Kalman filter is adopted in a myriad of applications for providing the minimum mean square error estimation of time-varying parameters in a simple and systematic manner. However, determining the Kalman filter performance is not so straightforward, particularly when process noise is present. In that case, one must often resort to numerical evaluations of the recursive Bayesian Cramér–Rao bound, or alternatively to implement the filter and assess the performance through Montecarlo simulations. This letter is intended to circumvent this limitation. It proposes a closed-form approximation for the steady-state performance of a Kalman filter based on a second-order dynamic model, while at the same time providing a novel closed-form upper bound for the convergence time. These two results are obtained by reformulating the Kalman filter in batch mode and analyzing the inner structure of the Bayesian information matrix. Simulation results are provided to illustrate the goodness of the proposed approach.
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  • 41
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: Presents the introductory editorial for this issue of the publication.
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  • 42
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: Measurement of the quality factor of a reverberation chamber has been examined using numerical simulation and experimental measurements. The numerical simulations demonstrate that common frequency-domain and time-domain approaches yield the same measured quality factors, provided that the measurement bandwidths of each approach are equal and the frequency-domain measurements are accurately compensated for antenna-efficiency effects. Measurements performed using intentionally mismatched antennas eliminate the antenna loading effects and give the quality factor of the chamber itself. The experimental validation confirms that the frequency-domain and time-domain approaches yield the same measured quality factors under practical conditions when the antennas are well-to-moderately matched. However, the accuracy of the frequency-domain measurement is compromised when large antenna-efficiency compensation must be applied when using poorly matched test antennas. The narrowband time-domain approach with poorly matched antennas provides consistent and repeatable measurements of the quality factor of the chamber itself without antenna loading effects.
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  • 43
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: In the context of printed circuit design, microstrip interconnects pose a great challenge in terms of radiated emission, signal integrity, and intertrace interference. Curved and bent microstrip lines are integral part of such high-frequency circuit design. In this paper, internal fields of an arbitrarily curved microstrip line are calculated using a sequential mode matching technique with piecewise circular discretization. Transverse asymmetry of the electric field is observed due to unequal curvatures of the two side edges of the microstrip line. A dynamic co-ordinate system based on Serret–Frenet reference frame is developed. A simple transmission line model is formulated in this new co-ordinate system to calculate the radiated far fields from the line. The developed model is applied to compute radiation from a sinusoidal line as well as that of a planar spiral. The model is also applied to compute the radiation efficiencies from various microstrip bends and it is observed that circular bends exhibit minimum leakage amongst others. A sinusoidal line and a planar spiral are fabricated and measured. Results are shown to be in good agreement with those predicted by the analytical model.
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  • 44
    Publication Date: 2018-01-10
    Description: An in situ (internal) electric field is used as a dosimetric quantity for human protection from low-frequency electromagnetic fields (lower than 5 MHz) under international safety standard/;guidelines. The IEEE standard uses a homogenous elliptical cross section to derive external field strength corresponding to an in situ field strength, while the International Committee on Non-Ionizing Radiation Protection (ICNIRP) guidelines use anatomical models to relate them. In the latter, “the 99th percentile value of the in situ electric field averaged over the cube of its side length of 2 mm” is used to represent the maximum in situ electric field. This metric was introduced to suppress computational artifacts that are inherent when using voxelized anatomical models, in which curved boundaries are discretized with a stair-casing approximation. To suppress the error, a few schemes have been proposed for treating the computational artifacts. In this study, the various schemes to suppress the artifacts are reviewed. Subsequently, a postprocessing method for determining the appropriate maximum in situ field strength is proposed. The performance of the proposed scheme is first verified by comparison with an analytical solution in a multilayered sphere. The method is then applied for different exposure scenarios in anatomically realistic human models where the volume under computation is also considered.
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  • 45
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    Publication Date: 2018-01-10
    Description: The continuous trend toward the miniaturization of modules, comprising high sensitive devices along with noisy circuits like wireless transceivers and digital core blocks, has led us to investigate the effect of disturbances on analog front-end circuits used in system-in-package modules. In this context, this paper focuses on the distortion of radio frequency interference in CMOS current feedback instrumentation amplifiers like those used in MEMS readout circuits. The way baseband signals are distorted by such amplifiers, when the interference is superimposed onto the input signals, is analyzed referring to a math model, to computer simulations and to measurements carried out on a test chip designed and fabricated specifically for this purpose.
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  • 46
    Publication Date: 2018-01-10
    Description: This paper investigates the radio frequency (RF)-induced heating in American Society for Testing and Materials phantom with a generic external fixation device for both birdcage (BC) coil and transverse electromagnetic (TEM) coil. Two typical orientations, i.e., fixture bar perpendicular to and parallel to the coil axis, have been considered. To compare the specific absorption rate and temperature rise in the two different RF coils at 3 T, both electromagnetic and thermal simulations were performed. It is found that tibia external fixation device with orientation parallel to the coil axis will induce severe heating effect in both coils. However, pelvic external fixation device induces larger heating level in TEM coil than BC coil. Furthermore, increasing the pin length or pin spacing of the pelvic external fixation device will cause a larger heating level in TEM coil, while such changes have no substantial effects on BC coil. We show that the transversely distributed electric field in TEM coil forms the underlying reason why pelvic external fixation device induces a higher heating level in TEM coil than BC coil. This finding also indicates that metallic external fixation devices with large dimensions along transverse direction, while might be safe in BC coil, can experience significant heating issue in TEM coil.
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  • 47
    Publication Date: 2018-01-10
    Description: Modeling the electromagnetic radiation from modern digital systems—acting effectively as extended stochastic sources as part of a complex architecture—is a challenging task. We follow an approach here based on measuring and propagating field-field autocorrelation functions (ACFs) after suitable averaging. From the modeling side, we use the Wigner transform of the ACFs to describe random wave fields in terms of position and direction of propagation variables. An approximate propagator for the components of the radiated magnetic field is constructed for these ACFs based on a linear flow map. Field-field ACFs at the aperture level are obtained from scanning measurements of complex sources. Distance and spatial resolution of the scanning plane is less than a wavelength from the source plane to capture the imprint of evanescent waves in the near-field ACFs. Near-field scanning and efficient near-to-far-field propagation is carried out and compared with measurements. Results of this study will be useful to assist far-field predictions, source reconstruction, and emission source microscopy.
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  • 48
    Publication Date: 2018-01-10
    Description: The purpose of this paper is to demonstrate the use of an optimized parallel feeding system to achieve low magnetic field in the overhead-feeder-type dc rail system. Traction conductors for electrified railways often produce very high electromagnetic fields especially at locations close to the railway, consequently posing an electromagnetic interference threat to any sensitive neighboring systems. This paper describes a technique for reducing the magnetic fields generated by the traction conductors, to as low as a few milliGauss, for achieving electromagnetic compatibility in a dc rail system design. It also shows how the optimization of the rail system conductors’ cross section, especially the feeder cables, can improve cancellation of the generated magnetic fields.
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  • 49
    Publication Date: 2018-01-10
    Description: This paper proposes a method for efficient identification of instruction-dependent sources on a printed circuit board (PCB) by localizing magnetic field sources from a limited number of measurements around the PCB. We first excite the processor by generating an artificial leakage signal at a specific frequency that is directly related to processor instructions. Then, we collect all three components of the magnetic field, but only at locations around the edge of the board. Furthermore, we model these magnetic field sources and then solve a forward–backward optimization problem using the model and measured data to identify the locations of the magnetic field sources, the magnitudes of the moments, and their orientations. The localization results are first verified using simulations, then tested when noise is added to the simulation results, and finally verified against measurements on field-programmable gate array (FPGA) and internet of things (IoT) development boards. The results show that the number of strong magnetic field sources on a board depends on the instructions used to excite the board. Furthermore, the results show that the proposed localization algorithm can accurately identify those sources, regardless of the frequency at which the measurements are conducted and the instruction pairs that are executed. Finally, the proposed method can significantly reduce the number of measurement points and the time needed to identify magnetic field sources on a PCB.
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  • 50
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    Publication Date: 2018-01-10
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    Print ISSN: 1527-3342
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  • 51
    Publication Date: 2018-01-10
    Description: The impact of spectral phase noise on the temporal pulse contrast is explored experimentally by using two zero-dispersion stretchers (Offner stretcher and two-lens stretcher). The results show clearly that a long temporal pedestal appears when there exists far-field spectral phase noise, which greatly degrades the pulse contrast. In our proof-of-principle experiment, by using a two-lens stretcher, the far-field spectral phase noise is avoided and the noise pedestal of the amplified pulse in a Nd:glass laser system is reduced, with the contrast reaching a level of 10 –11 in the 60-ps time window before the main pulse. This simple method may pave the way in a PW-level Nd:glass laser by directly using pre-cleaning techniques.
    Print ISSN: 1077-260X
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  • 52
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    Publication Date: 2018-01-10
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  • 53
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    Publication Date: 2018-01-10
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  • 62
    Publication Date: 2018-01-10
    Description: We present a detailed frequency noise characterization of an ultrafast diode-pumped solid-state laser operating at 25-GHz repetition rate. The laser is based on the gain material Er:Yb:glass and operates at a wavelength of 1.55 μm. Using a beating measurement with an ultralow-noise continuous-wave laser in combination with a dedicated electrical scheme, we measured the frequency noise properties of an optical mode of the 25-GHz laser, of its repetition rate and indirectly of its carrier-envelope offset (CEO) signal without detecting the CEO frequency by the standard approach of nonlinear interferometry. We observed a strong anticorrelation between the frequency noise of the indirect CEO signal and of the repetition rate in our laser, leading to optical modes with a linewidth below 300 kHz in the free-running laser (at 100-ms integration time), much narrower than the individual contributions of the carrier envelope offset and repetition rate. We explain this behavior by the presence of a fixed point located close to the optical carrier in the laser spectrum for the dominant noise source.
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  • 63
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: In this letter, we propose a strategy to enhance absorption in the black phosphorus absorber based on a nanocavity structure. By introducing a porous silver layer, an enhanced broadband light absorption can be obtained in the spectral range of 520–820 nm. The optical characteristics of the black phosphorus absorptive layer are thoroughly analyzed by absorption spectra, electric intensity distribution, and power flow distribution. Numerical and analytical analysis revealed that the optical absorption of the black phosphorus layer with a porous silver layer can be enhanced by 50% and 396% at the resonant wavelength of 690 nm for p-polarized and s-polarized incidences, respectively, when compared to that without a silver layer. Furthermore, the short-circuit current density ( $J_{{rm{SC}}}$ ) was calculated for the proposed architecture. The peak value of $J_{{rm{SC}}}$ was more than 18 mA/cm 2 . It is demonstrated that this super absorption structure could find important applications on plasmonic-assisted photovoltaic devices or other opto-electronic devices, which will promote the development of ultrathin on-chip energy harvesting and new thin-film active devices.
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  • 64
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    Publication Date: 2018-01-10
    Description: We proposed an improved phase-based method by using a filtering window on the low-coherence interferogram. Through theoretical derivation and numerical simulation, we prove the correction of our proposed method that the fringe phase can be demodulated nondestructively after applying a symmetrical filtering window nearby the envelope peak, and our method can enhance system SNR. Since fringe overlap phenomenon arising from narrow bandwidth occurs frequently in single-mode sensing system, this method is especially applicable to remote sensing wherein the localization of interference fringe is difficult using traditional phase-based methods. To verify this method, an experiment with a single-mode fiber Fabry-Perot air pressure sensing system was carried out. The experiment results showed that the precision using our method decreased to less than 0.053 $%$ in full 280 kPa pressure scale and the sensing distance extended to 20 km, which were apparently superior to traditional phase-based methods.
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  • 65
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: A new phase retrieval technique in digital holographic microscopy (DHM) with three defocused holograms is proposed. Given the defocusing distance, the phase distributions of tested specimen can be reconstructed with a simple algebraic equation. We have deduced this equation in detail. To avoid the manual operation, the defocused holograms can be flexibly and precisely obtained by introducing an electronically tunable lens based 4f system. This method is suitable for an on-axis hologram as well as the off-axis one but avoids the requirements for not only the iterative process, complex spectrum selection in off-axis DHM or additional phase-shifting devices in on-axis DHM but also the assumption of tested specimen or previous knowledge of the system. A series of simulations and the experimental results of the microlens array and water drop demonstrate the feasibility and effectiveness of the proposed method.
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  • 66
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    Publication Date: 2018-01-10
    Description: One of the most important applications of THz frequencies is biomedical sensing. However, in a THz range, surface plasmon waves on flat metals are not confined and therefore cannot be used for subwavelength sensing. But, it has been shown that graphene can support surface waves at THz frequencies, which has similar properties as plasmonic waves in an optical range. In this paper, a highly sensitive gas sensor in the terahertz frequencies by exciting surface plasmon resonance (SPR) of graphene is proposed. The results show that the proposed SPR gas sensor has high stability and high sensitivity ( S ), and the highest S max (∼147°/RIU) has been obtained by optimizing the Fermi energy, the thickness of the dielectric layer, and the incident light frequency. Moreover, the S of the proposed THz sensor for different refractive index (RI) of gas sensing medium ( n 1 ) is also discussed.
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  • 67
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    Institute of Electrical and Electronics Engineers (IEEE)
    Publication Date: 2018-01-10
    Description: Binocular stereo vision (BSV) system has been widely used in various fields, such as intelligent manufacture, smart robot, and so on. However, the location accuracy of the current BSV still cannot fully satisfy industry requirements due to lack of a parameters optimization BSV system. In this paper, a high accuracy BSV system is proposed. This is achieved through analyzing the seven parameters of the BSV system, which are classified into two groups: system structure parameters (SSPs) and camera calibration parameters (CCPs). For the SSPs, an improved analysis model is designed to expose the possible errors caused by three parameters. Furthermore, a new correlation model among them is also proposed to analyze the errors caused by their correlation. On the other hand, for the CCPs, the orthogonal experiment model is employed for selecting the optimal combination of the four calibration parameters. Meanwhile, the weight among the four parameters is also analyzed for reducing errors. Finally, the effectiveness of our proposed method is demonstrated by a large number of experiments. It gives a useful reference to the BSV system used in applied optics research and application fields.
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  • 68
    Publication Date: 2018-01-10
    Description: We propose an all-optical virtual private network (VPN) supporting dynamic bandwidth allocation (DBA) in an orthogonal frequency division multiple access-based passive optical network. A microwave photonic bandpass filter (MP-BPF) is used to transmit the VPN signal without electrical conversion. The DBA is implemented by adjusting a free spectral range of the MP-BPF with corresponding subcarrier allocation. A RF clipping-tone (CT) is used to stabilize the optical channel suffered from phase induced-intensity noise and Rayleigh back-scattering noise. The DBA is experimentally verified at different two DBA scenarios in 20-km single-fiber loopback link in terms of channel error vector magnitude, spectral efficiency after adaptive modulation. Due to the CT-based channel stabilization, achievable spectral efficiency could be improved, and the feasibility of the proposed system is successfully demonstrated.
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  • 69
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    Publication Date: 2018-01-10
    Description: The exponential growth of network traffic within data centers and high-performance computing generates a growing volume of fiber cabling. This raises the need for spectrally efficient communication scheme, which allows easy integration of optics and electronics. In this paper, we suggest a mode group division multiplexing scheme based upon intensity-modulated silicon photonics (SiP) Mach–Zehnder modulators (MZMs) coupled to standard graded-index multi-mode fiber directly detected using multi-segment concentric photo-detector. In addition, we have theoretically derived the bit and power loading of such a system in a closed-loop multiple-input multiple-output (MIMO) formation using convex optimization with two possible types of architectures: the vertical Bell Labs layered space-time architecture (V-BLAST) with minimum mean square error and successive interference cancellation (MMSE-SIC); and singular value decomposition (SVD). Our optimization problem maximizes the system's capacity under peak amplitude, power consumption, and BER constraints. Simulation results have shown the superiority of a V-BLAST MMSE-SIC over the SVD architecture in terms of total spectral efficiency for a 4 × 4 MIMO short reach low driving voltage conventional SiP-based MZM system.
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  • 70
    Publication Date: 2018-01-10
    Description: A novel multichannel free-space optical (FSO) communication system based on orbital angular momentum (OAM) carried by frozen waves with different longitudinal patterns is studied in this paper. The longitudinal OAM multiplexing (LOAMM) system is simulated under atmospheric turbulence, which is based on the split-step Fourier transform method and includes multiple random phase screens. The influences of system parameters on the average OAM mode probability densities are analyzed and discussed, such as propagation distance, strength of turbulence, sizes of finite aperture function, OAM mode numbers, and source parameters. It is found that in the limited apertures, the detection probability spectrum of the LOAMM system is inversely proportional to OAM mode numbers, strength of turbulence, and propagation distance. The bit-error rate and aggregate capacities are compared between the traditional OAM-based space-division-multiplexing (OAM-SDM) system with Bessel beams and our proposed LOAMM system. Our work should contribute to proving that the LOAMM system has a number of advantages over the OAM-SDM system in FSO communication.
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  • 71
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    Publication Date: 2018-01-10
    Description: In recent years, digital pre-distortion has emerged as a powerful approach to compensate linear and non-linear imperfections of the transmitter. Previous solutions are either based on factory calibration or use a local auxiliary receiver. Here, we present a digital pre-distortion architecture to compensate transmitter frequency response and I/Q skew, which relies upon a feedback from the far-end receiver and uses the signal propagated over the optical link. The effectiveness of the proposed solution is validated over different transmission systems for dual-polarization 64 QAM net 400 Gb/s and 16 QAM net 200 Gb/s signals.
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  • 72
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    Publication Date: 2018-01-10
    Description: The tuning of transmission response of an optical microring resonator (MRR) always associates with significant shift of the resonant wavelength, which leads to serious problems for most of applications. In this letter, we demonstrate that the Mach–Zehnder-interferometer (MZI)-coupled microring resonators with asymmetric directional couplers in the MZIs could still have large magnitude and phase tuning range, while maintaining the resonant wavelength unchanged. An add-drop MZI-coupled microring resonator with asymmetric directional couplers is fabricated on a silicon-on-insulator chip, and the measurement agrees well with the theoretical prediction. Our study would be interesting to photonic integrated circuits, which require tunable MRRs.
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    Publication Date: 2018-01-10
    Description: A discrete-mode laser diode, fabricated in the In0.6Ga0.4P/AlGaInP multiple quantum well system, emitting a single mode at $lambda =689$ nm is reported. The laser has an ex-facet output power >10 mW at 30 °C and operates mode hop free in the temperature range 0 °C to 50 °C.
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    Publication Date: 2018-01-10
    Description: Single longitudinal mode emission of laterally coupled distributed-feedback (LC-DFB) laser diodes (LDs) based on InGaN/GaN multiquantum-well structures containing 10th-order surface Bragg gratings with V-shaped grooves is demonstrated. The gratings were fabricated alongside a 2- $mu text{m}$ -wide contact stripe by i-line stepper lithography and inductively coupled plasma etching. A single peak emission at 404.6 nm with a full-width at half-maximum of 0.04 nm was achieved at an output power of about 46 mW under pulsed laser operation. The shift of the lasing wavelength of LC-DFB LDs in the temperature range from 22 °C to 45 °C was around three times smaller than that of comparable ridge waveguide Fabry–Pérot LDs.
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    Publication Date: 2018-01-10
    Description: We designed a terahertz bandpass filter based on double-layer frequency selective surface. Details of the proposed terahertz wave filter design and of the related parametric analysis are presented and discussed. The proposed terahertz filter was fabricated by laser technology. The transmission spectrum was characterized by terahertz time-domain spectroscopy. The results show that the center frequency of the terahertz filter is about 1 THz with 3-dB bandwidth of 400 GHz.
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    Publication Date: 2018-01-10
    Description: We experimentally demonstrate a fiber-based reconfigurable system for programming the envelope of high-speed optical pulse train by using fractional-rate multilevel amplitude modulation. Amplitude-modulated optical pulse trains undergo the discrete Fourier transform (DFT) realized by the temporal Talbot effect in a dispersive fiber. Consequently, rate-multiplied optical pulse trains with programmable envelopes can be achieved. In this letter, we report experimental synthesis of ~80-GHz optical pulse trains with expectant binary patterns, parabolic, square, and triangular envelopes. We also consider practical implementation issues and numerically analyze the influence from the deviation of modulation coefficients and finite extinction ratio of the Mach–Zehnder modulator on the generated pulses.
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    Publication Date: 2018-01-10
    Description: We propose an electrically driven electro-optical modulator integrated with the phase-change material Ge 2 Sb 2 Te 5 (GST). This modulator incorporates a hybrid Si-GST-Cu waveguide with input and output Si waveguides. For the waveguide modulator with an active segment of $0.2~mu text{m}^{2}$ , the switched phase is stable with off/on extinction ratios of >5.4 dB on the entire ${C}$ -band. Since the phase change of GST only consumes energy during the stated transitions, the energy consumption per bit for this nanosize device is ideally low on the order of sub-nJ per cycle.
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  • 78
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    Publication Date: 2018-01-10
    Description: A novel approach for measuring the microwave Doppler frequency shift (DFS) based on a dual-drive Mach–Zehnder modulator (DDMZM) is proposed and demonstrated. The value and direction of the DFS can be simultaneously measured with high precision by using a reference signal. In the DDMZM, the transmitted signal and reference signal are applied to one radio frequency (RF) port, while the echo signal is applied to the other RF port. Then, the generated optical signals are sent to a low-speed photodetecter, and the beat frequency between the transmitted and echo signals is equal to the value of DFS, while the direction of DFS can be distinguished by comparing the two beat frequencies generated by the transmitted signal with reference signal and the echo signal with reference signal, respectively. The DFS from −100 to +100 kHz at the carrier frequency of 10, 14, and 18 GHz is successfully measured, and the maximal error is less than 1.0 Hz.
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    Publication Date: 2018-01-10
    Description: We demonstrate that using a broadband, first order, and coherent pump laser enables effective and efficient forward-pumped distributed Raman amplification for long-haul transmission systems, thanks to the simultaneous suppression of ASE noise and RIN-related penalty. We show in both experiments and simulation that this scheme extends the reach of $10times120$ Gb/s DP-QPSK WDM transmission by a minimum of 50%, compared with low RIN Bi-doped fibre laser and other commercially available pump lasers. Moreover, it requires very low forward pump power, and maintains uniform/symmetric signal power distribution which allows effective nonlinearity compensation.
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    Publication Date: 2018-01-10
    Description: In this letter, monolithic red, green, and blue (RGB) micro light-emitting diodes (LEDs) were fabricated using gallium nitride based blue micro LEDs and quantum dots (QDs). Red and green QDs were sprayed onto individual region surrounded by patterned black matrix photoresist on the blue micro LEDs to form color conversion layers. Owing to its light-blocking capability, the patterned black matrix photoresist improved the contrast ratio of the micro LEDs from 11 to 22. To enhance the color conversion efficiency and the light output intensity, a hybrid Bragg reflector (HBR) was deposited on the bottom side of the monolithic RGB micro LEDs, thus reflecting the RGB light emitted to the substrate. To further improve the color purity of the red and green light, a distributed Bragg reflector (DBR) with high reflection for the blue light was deposited on the top side of the QDs/micro LEDs. The red and green light output intensities of the micro LEDs with HBR and DBR were enhanced by about 27%.
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    Publication Date: 2018-01-10
    Description: We proposed an improved femtosecond optical Kerr gate with double gate pulses (DOKG) using a femtosecond laser, in which an ultrashort switching time can be realized even when a relatively slow response optical Kerr medium of carbon disulfide was used. The results showed that when the time delay and the light intensity ratio of the two pump pulses were adjusted to be about 140 fs and 1:0.9, the switching time and the maximum transmission efficiency of the DOKG could be optimized to be about 130 fs and 37%. The DOKG is convenient to be built and offers a good choice for applications based on ultrafast optical switch.
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    Publication Date: 2018-01-10
    Description: We describe and experimentally evaluate a stabilized radio-frequency transfer technique that employs optical phase sensing and optical phase actuation. This technique is achieved by modifying existing optical frequency transfer equipment and also exhibits advantages over previous stabilized radio-frequency transfer techniques in terms of size and complexity. Acousto-optic modulators (AOMs) are used to modulate an optical carrier. Stabilization of frequency fluctuations in the link is achieved by steering the frequency of one of the AOMs. We demonstrate the stabilized transfer of a 160-MHz signal over a 166-km fiber optical link, achieving an Allan deviation of $9.7times 10^{-12}$ at 1 s of integration, and $6.4times 10^{-15}$ at $10^{4}$ s. This technique was considered for application to the Square Kilometre Array SKA1-low radio telescope.
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    Publication Date: 2018-01-10
    Description: Energy involves everybody. Current changes in energy and power systems, including the distributed production of renewables, an increasing need for flexibility of operations, and energy storage and transmission, affect consumers in one way or another. Changes often require the active participation and support of consumers, who may become prosumers. All the new systems and technologies developed by electrical engineers may influence consumer behavior and trigger positive or negative responses. Hence, it is important for electrical engineers to understand how their work may affect consumers, which behavior changes their solutions involve, and which consumer needs and preferences must be considered when developing new technology. This issue encourages a conversation among electrical engineers and social scientists and facilitates the integration of their different expertise.
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