Polarization Channels Research Articles

Flexoelectricity on the photovoltaic and pyroelectric effect and ferroelectric memory of 3D-printed BaTiO3/PVDF nanocomposite

Ferroelectric memories show great potential in applications of portable electronics due to low power consumption, high reliability and fast response speed. Therefore, non-destructive readout of ferroelectric memories using the ferroelectric photovoltaic effect attracted tremendous research attention. In this investigation, flexoelectric-enhanced photovoltaic effect (FPV effect) were systematically investigated in curved 3D-printed BaTiO3/PVDF composite films. In the bending process, a strain gradient field was formed between the BaTiO3 (BTO) particles, which led to a relatively large flexoelectric effect. Compared with that of pristine PVDF, the flexoelectric coefficient of BTO/PVDF-15 (15% BTO) was increased 3.7-fold to 2.65 × 10−9 C/m. Furthermore, we found that the photovoltaic current Ipv of the BTO/PVDF-15 (15% BTO) composite film increased by 3.4 times compared with the pristine PVDF film at the same curvature. This is mainly attributed to the FPV effect. In addition, “polarization channels” were found for the first time inside nanocomposite materials using the flexoelectricity effect through 2D phase-field simulations, and the channels can be artificially controlled by simply bending the film. Most importantly, the BTO/PVDF-based composite film was designed as flexible ferroelectric memories. We demonstrated for the first time that the intensity difference of the signal for 0 and 1 of the BTO/PVDF-based memories were more than 10 times, which can be read directly using a laser. This investigation shows great promise that flexoelectricity in piezoelectric polymer nanocomposite can greatly benefit the nondestructive readout of ferroelectric memory devices.

Shortwave Infrared Multi-Angle Polarization Imager (MAPI) Onboard Fengyun-3 Precipitation Satellite for Enhanced Cloud Characterization

Accurate measurement of the radiative properties of clouds and aerosols is of great significance to global climate change and numerical weather prediction. The multi-angle polarization imager (MAPI) onboard the Fengyun-3 precipitation satellite, planned to be launched in 2023, will provide the multi-angle, multi-shortwave infrared (SWIR) channels and multi-polarization satellite observation of clouds and aerosols. MAPI operates in a non-sun-synchronized inclined orbit and provides images with a spatial resolution of 3 km (sub-satellite) and a swath of 700 km. The observation channels of the MAPI include 1030 nm, 1370 nm, and 1640 nm polarization channels and corresponding non-polarization channels, which provide observation information from 14 angles. In-flight radiometric and polarimetric calibration strategies are introduced, aiming to achieve radiometric accuracy of 5% and polarimetric accuracy of 2%. Simulation experiments show that the MAPI has some unique advantages of characterizing clouds and aerosols. For cloud observation, the polarization phase functions of the 1030 nm and 1640 nm around the scattering angle of a cloudbow show strong sensitivity to cloud droplet radius and effective variance. In addition, the polarized observation of the 1030 nm and 1640 nm has a higher content of information for aerosol than VIS-NIR. Additionally, the unique observation geometry of non-sun-synchronous orbits can provide more radiometric and polarization information with expanded scattering angles. Thus, the multi-angle polarization measurement of the new SWIR channel onboard Fengyun-3 can optimize cloud phase state identification and cloud microphysical parameter inversion, as well as the retrieval of aerosols. The results obtained from the simulations will provide support for the design of the next generation of polarized imagers of China.

Direction-sensitive rotational speed measurement based on the rotational Doppler effect of cylindrical vector beams.

The Doppler effect has inspired numerous applications since its discovery, initially enabling measurement of the relative velocity between a moving object and a wave source. In recent years, it has been found that scalar vortex beams with orbital angular momenta can produce the rotational Doppler effect, which can be used to measure the rotational speeds of rotating objects. However, in practice, only the absolute value of the rotational Doppler frequency shift can be obtained, and it is difficult to distinguish the direction of the object directly by a single measurement. This difficulty can be solved by using cylindrical vector beams with spatially varying polarization states. The cylindrical vector beam is formed by coaxial superposition of two vortex beams with opposite orbital angular momenta and orthogonal polarization states. By using two different polarization channels, the rotation direction can be directly recognized according to the relative phase difference between the two channels. In this paper, the scattering point model is employed to analyze the rotational Doppler effect of cylindrical vector beams, and a variety of cylindrical vector beams are generated by using vortex half-wave plates. The scheme can realize measurement of the rotational speed and direction simultaneously, and the system has simple construction, high accuracy of angular velocity measurement, and accurate direction identification.

Application of Multi-Measurement Vector Based on the Wireless Sensor Network in Mechanical Fault Diagnosis

In order to solve the problem of low positioning accuracy of mechanical fault diagnosis, a polarization GPR imaging reconstruction algorithm based on the MMV model was proposed. The algorithm was mainly based on the joint processing of the measured data of multiple polarization channels to achieve the reconstruction of the reflectance of the detection scene corresponding to each polarization channel. The simulation data processing results based on FDTD showed that compared with the traditional SMV model polarization imaging algorithm, the proposed imaging algorithm could improve the accuracy of target location reconstruction and the ability of background clutter suppression significantly. Compared with the SMV model, TCR obtained by the MMV model increased by 30%. As for the imaging results at different noise ratios, TCR obtained by the MMV model was 10% higher than that obtained by the SMV model. And when the ratio of available real data samples decreased to 25%, the sample data generation based on the adversarial generation network could greatly improve the classification accuracy of the fault diagnosis model. It could realize the detection of the target better, so as to locate faults accurately.

Improving the phase reconstruction accuracy of simultaneous phase-shifted lateral shearing interferometry using a polarization redundant sub-region interpolation method.

In a simultaneous phase-shifted lateral shearing interferometry, a division of focal plane polarization camera is generally used as the phase-shifting device. However, acquiring simultaneous phase-shift interferograms in a single frame suffers from a lack of spatial resolution, significantly affecting the phase reconstruction accuracy. A polarization redundant sub-region interpolation (PRSI) method is proposed to solve this problem. This interpolation method distinguishes smooth regions from stripe fringe regions by calculating the polarization redundancy error of the synchronous phase shift interferogram. After sub-regional processing, resolution reconstruction is performed in the smoothed area using a fast convolutional bilinear interpolation method. In the streak detail region, the resolution reconstruction is performed based on the strength of the correlation between the orthogonal and non-orthogonal polarization channels crossing the streak region. The PRSI method can quickly reconstruct the lost pixels and accurately recover the stripe detail information. Experiment results show that the proposed interpolation method outperforms the existing dominant methods in terms of visual reconstruction effect and quantitative index of phase reconstruction.

LSDNet: Lightweight CNN Model Driven by PNF for PolSAR Image Ship Detection

Polarimetric synthetic aperture radar (PolSAR) as an active microwave imaging device employing pulse compression technology to obtain echo information of multiple polarization channels has been widely used in marine target detection. However, the detection of ship targets in PolSAR images is often disturbed by clutter interference, such as side lobes, ghost ships, etc. Additionally, the current common convolutional neural network object detection models are accompanied by a large number of parameters, thereby, their performance is greatly limited by available datasets. Therefore, aiming at solving the above questions, we propose a lightweight ship detection model driven by a polarimetric notch filter (PNF) feature for PolSAR ship detection. First, considering the scattering mechanism of target and clutter, the PNF feature is constructed with geometric perturbation information to overcome the vulnerability of existing amplitude feature-driven-based detectors to clutter interferences. Then, a lightweight ship detection network (LSDNet) is proposed, which uses a limited multilayer convolutional structure supported by a small-scale dataset and introduces dilated convolution during the extraction of high-level features to achieve spatial feature perception of weak and small ship targets. Finally, combined with the region-based fully convolutional head network, the model parameter is further reduced while training and inference efficiency is accelerated. Experimental results on a substantial number of PolSAR images show that the PNF-driven LSDNet model is better than the state-of-the-art detection models in terms of accuracy and efficiency, whose parameter quantity is 41.04% less than that of Faster R-CNN and achieves 0.92 of F1 Score and 0.9683 of average precision.

A Dual-Polarized Reconfigurable Reflectarray Antenna Based on Dual-Channel Programmable Metasurface

The concept of dual-polarized reconfigurable reflectarray (RRA) featuring dual-polarized beam control is proposed and demonstrated using a dual-channel programmable metasurface. The p-i-n diodes are incorporated into each metasurface element as the active components to provide independent phase control in two orthogonal polarization channels. By altering the working states of each p-i-n diode, well-defined beam scanning can be obtained. Element design, focal diameter ratio selection, and discretized phase distributions are carefully optimized to ensure stable radiation performance of the proposed RRA. As verification, a prototype consisting of 20 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times20$ </tex-math></inline-formula> elements is fabricated and measured, which is controlled by a field programmable gate array-based controller. Measured results show that wide-angle beam scanning up to ±40° can be obtained around 7.45 GHz, with peak gains of 21.13 and 20.89 dBi in dual channels, corresponding to aperture efficiencies of 16.35% and 15.47%. The proposed dual-polarized RRA brings a new freedom in polarization manipulations for versatile beam scanning, which provides promising applications in wireless communication and tracking/detecting systems.

Metasurface-based augmented reality headset equipped with an eye movement monitoring system

In this paper, a metasurface-based waveguide display equipped with an eye movement monitoring system is presented. In the suggested device, the functions of the eye movement system and AR are completely independent of each other and are designed in two separate sections at wavelengths 775 nm and 635 nm respectively. In the next part, in order to investigate the effects of the shape of the waveguide on FOV and efficiency, a multifunctional display system comprise of a single rectangular waveguide with two sensitive polarization channels are designed to operate as an AR and eye movement monitoring systems simultaneously at visible and IR wavelengths respectively. In both devices, monitoring eye movements can be done over the range of − 24° to 24° and the digital images are displaced in the user’s FOV based on horizontal eye positions. Although the first suggested system is heavier than one, its FOV is almost more than twice of the second system. The results indicate that metasurface-based waveguide technology can be considered as an appropriate platform for developing wearable eye movement systems.

Deformation Monitoring of Tailings Reservoir Based on Polarimetric Time Series InSAR: Example of Kafang Tailings Reservoir, China

Safe operation of tailings reservoirs is essential to protect downstream life and property, but current monitoring methods are inadequate in scale and refinement, and most reservoirs are built in low coherence areas far from cities. Use of polarization data to monitor deformation may improve area coherence and thus point selection density. With the example of the Kafang tailings reservoir and dual-polarization Sentinel-1 data from 9 August 2020 to 24 May 2021, homogeneous points of different polarization channels were identified with the hypothesis test of the confidence interval method. Results were fused, and BEST, sub-optimum scattering mechanism (SOM), and equal scattering mechanism (ESM) methods were used to optimize phase quality of persistent scatterer (PS) and distributed scatterer (DS) pixels and obtain more detailed deformation information on the area with time series processing. The fusion of homogeneous point sets obtained from different polarization intensity data increased the number of homogeneous points, which was 3.86% and 8.45% higher than that of VH and VV polarization images, respectively. The three polarization optimization methods improved point selection density. Compared with the VV polarization image, the high coherence point density increased by 1.83 (BEST), 3.66 (SOM), and 5.76 (ESM) times, whereas it increased by 1.17 (BEST), 1.84 (SOM), and 2.04 (ESM) times in the tailings reservoir. The consistency and reliability of different methods were good. By comparing the monitoring results of the three methods using polarization data, the hypothesis test of the confidence interval (HTCI) algorithm, and the polarization optimization method will effectively increase the point selection number of the study area, and the ESM method can show the deformation of tailings area more comprehensively. Monitoring indicated deformation of the tailings reservoir tended to diffuse outward from the area with the largest deformation and was relatively stable.

Compensation for the ionospheric dispersion effect on spaceborne P-band full-polarimetric wideband SAR

ABSTRACT Spaceborne P-band full-polarimetric wideband synthetic aperture radar (SAR) will be affected by ionospheric phase dispersion and polarimetric dispersion. An improved contrast optimization autofocus (COA) method using four polarization channel data is proposed to compensate for both phase dispersion and polarimetric dispersion. The basis and steps of the method are given. Its performance is analysed by typical target simulation under clutter background and compared with traditional COA method for single channel. The residual quadratic phase error (QPE) of single channel compensated by traditional method may exceed 45° focusing threshold, while the proposed method can reduce the error to less than 10°. Due to the lack of spaceborne P-band SAR data, we simulate the effect of ionosphere on P-band SAR based on ALOS2 PALSAR2 data and verify the proposed method. The simulation result shows the proposed method is effective and superior to traditional method.

End-to-end metasurface inverse design for single-shot multi-channel imaging.

We introduce end-to-end inverse design for multi-channel imaging, in which a nanophotonic frontend is optimized in conjunction with an image-processing backend to extract depth, spectral and polarization channels from a single monochrome image. Unlike diffractive optics, we show that subwavelength-scale "metasurface" designs can easily distinguish similar wavelength and polarization inputs. The proposed technique integrates a single-layer metasurface frontend with an efficient Tikhonov reconstruction backend, without any additional optics except a grayscale sensor. Our method yields multi-channel imaging by spontaneous demultiplexing: the metaoptics front-end separates different channels into distinct spatial domains whose locations on the sensor are optimally discovered by the inverse-design algorithm. We present large-area metasurface designs, compatible with standard lithography, for multi-spectral imaging, depth-spectral imaging, and "all-in-one" spectro-polarimetric-depth imaging with robust reconstruction performance (≲ 10% error with 1% detector noise). In contrast to neural networks, our framework is physically interpretable and does not require large training sets. It can be used to reconstruct arbitrary three-dimensional scenes with full multi-wavelength spectra and polarization textures.

Floating small target detection based on the dual-polarization cross-time-frequency distribution in sea clutter

In this paper, a polarization fusion detection method based on dual-polarization cross-time-frequency distribution is proposed to improve the detection performance compared with the original TF-feature-based detector in floating target detection in sea clutter background. Utilizing the received echoes information from the dual-polarization channels, time-frequency distributions (TFD) of radar returns from each polarization channel and the cross-time-frequency distribution (CTFD) of the two channels are computed. Weighted geometric average based on the signal-to-clutter ratio (SCR) is used to calculate a weighted fusion TFD based on the TFDs and CTFD from dual-polarization channels. To observe differences between sea clutter and target precisely, normalized time-frequency distributions (NTFD) of the cell under test (CUT) are calculated by the mean and variance of the fusion TFD computed from the reference range cells adjacent to the CUT. And the three existing features, the ridge integration (RI), the number of connected regions (NR) and the maximal size of connected regions (MS) are extracted from the NTFD and the convexhull learning algorithm is used to construct a polarization fusion detector in the feature space. Analyses of experimental results on the recognized IPIX database show that the proposed polarization fusion detector obtains superior detection performance compared to the original TF-feature-based detector and has competitive detection performance compared to other existing excellent feature-based detectors.

Polarized Intensity Ratio Constraint Demosaicing for the Division of a Focal-Plane Polarimetric Image

Polarization is an independent dimension of light wave information that has broad application prospects in machine vision and remote sensing tasks. Polarization imaging using a division-of-focal-plane (DoFP) polarimetric sensor can meet lightweight and real-time application requirements. Similar to Bayer filter-based color imaging, demosaicing is a basic and important processing step in DoFP polarization imaging. Due to the differences in the physical properties of polarization and the color of light waves, the widely studied color demosaicing method cannot be directly applied to polarization demosaicing. We propose a polarized intensity ratio constraint demosaicing model to efficiently account for the characteristics of polarization detection in this work. First, we discuss the special constraint relationship between the polarization channels. It can be simply described as: for a beam of light, the sum of the intensities detected by any two vertical ideal analyzers should be equal to the total light intensity. Then, based on this constraint relationship and drawing on the concept of guided filtering, a new polarization demosaicing method is developed. A method to directly use raw images captured by the DoFP detector as the ground truth for comparison experiments is then constructed to aid in the convenient collection of experimental data and extensive image scenarios. Results of both qualitative and quantitative experiments illustrate that our method is an effective and practical method to faithfully recover the full polarization information of each pixel from a single mosaic input image.

Broadband Multichannel Cylindrical Vector Beam Generation by a Single Metasurface

AbstractBeams with spatially‐varying polarization states have been the topic of much interest recently due to the unusual ways in which they can interact with matter. Cylindrical vector beams (CVBs) represent the most commonly used type and feature cylindrically‐symmetric polarization distributions. The optical systems employed thus far for their generation have usually only been able to produce a single CVB. To generate and observe multiple CVBs, bulky optical systems with stringent alignment tolerances have been needed. Here, a method to generate an array of CVBs using a single optical element, namely a transmission‐mode dielectric metasurface, is demonstrated. The incident light is split into an array of left and right‐handed circularly polarized vortex beams that superpose with a controllable phase difference. An array of CVBs with 12 channels over a broad wavelength range is experimentally demonstrated. This study's method produces a significant increase in the number of polarization channels compared to previous reports and solves the long‐standing challenge of unequal intensity distributions. It furthermore improves the flexibility of the vector field control by not only generating CVBs of different orders but also controlling their polarization rotation. This method may pave the way for applications in optical communications, laser machining, and optical trapping.

Combined spectroscopy and intensity interferometry to determine the distances of the blue supergiants P Cygni and Rigel

ABSTRACT In this paper, we report on spatial intensity interferometry measurements within the Hα line on two stars: the Luminous Blue Variable supergiant P Cygni and the late-type B supergiant Rigel. The experimental setup was upgraded to allow simultaneous measurement of two polarization channels, instead of one in our previous setup, and the zero baseline correlation function on-sky to validate independent estimates obtained from the stellar spectrum and the instrumental spectral throughput. Combined with simultaneous spectra measurements and based on radiative transfer models calculated with the code CMFGEN, we were able to fit our measured visibility curves to extract the stellar distances. Our distance determinations for both P Cygni (1.61 ± 0.18 kpc) and Rigel (0.26 ± 0.02 kpc) agree very well with the values provided by astrometry with the Gaia and Hipparcos missions, respectively. This result for Rigel was obtained by adopting a stellar luminosity of L⋆ = 123 000 L⊙, which is reported in the literature as being consistent with the Hipparcos distance to Rigel. However, due to the lack of consensus on Rigel’s luminosity, we also explore how the adoption of the stellar luminosity in our models affects our distance determination for Rigel. In conclusion, we support, in an independent way, the distance to Rigel as the one provided by the Hipparcos mission, when taking the luminosity of 123 000 L⊙ at face value. This study is the first successful step towards extending the application of the Wind Momentum Luminosity Relation method for distance calibration from an LBV supergiant to a more normal late-type B supergiant.

Digital Polarization Programmable Metasurface for Continuous Polarization Angle Rotation and Radar Applications

Polarization angle manipulation has been a vital technic in radar applications. This paper proposes and demonstrates a digital polarization programmable metasurface for continuous polarization angle rotation and radar applications. By coding “0” and “1” elements with the two orthogonally polarized waves having 180° phase difference, the polarization angle of electromagnetic (EM) waves can be continually and arbitrarily manipulated. The designed metasurface adopts a patch-transmission and line-patch structure and integrates two polarization channels to carry out 1-bit coding. By rotating the azimuth angle of the designed metasurface mechanically, a continuous rotation of the polarization angle of the transmitted wave can be achieved. Moreover, the transmission around 9.4 GHz can reach higher than 95%. The metasurface sample with optimized structure parameters has been fabricated and tested, where the measurement agrees well with the simulation results. In addition, a radar detection experiment was implemented with an anisotropic target, demonstrating the practical use of the proposed metasurface for polarimetric radar.

BM3D-based denoising method for color polarization filter array.

Color split-focal plane polarization imaging systems are composed of image sensors with a color polarization filter array (CPFA). The noise generated during image acquisition leads to incorrect estimation of the color polarization information. Therefore, it is necessary to denoise CPFA image data. In this study, we propose a CPFA block-matching and 3D filtering (CPFA-BM3D) algorithm for CPFA image data. The algorithm makes full use of the correlation between different polarization channels and different color channels, restricts the grouping of similar 2D image blocks to form 3D blocks, and attenuates Gaussian noise in the transform domain. We evaluate the denoising performance of the proposed algorithm using simulated and real CPFA images. Experimental results show that the proposed method significantly suppresses noise while preserving the image details and polarization information. Its peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) indicators are superior to those of the other existing methods. The mean values of the PSNR and SSIM of the degree of linear polarization (DoLP) color images calculated through CPFA image interpolation can be increased to 200% and 400%, respectively, by denoising with the proposed method.

Performance Optimization of Polarized MIMO Relay Channels Based on the COST 2100 Channel Model

Polarization selectivity has a great impact on multiple-input–multiple-output (MIMO) relay channels. In this letter, the channel capacity of MIMO relay channels is analyzed, revealing the polarization dependency of multipath components. Polarization optimization schemes are proposed, including a regular optimization and a dynamic weight particle swarm optimization (DWPSO) for MIMO relay channels. The performance analysis shows that the DWPSO can significantly improve the link capacity of MIMO relay channels based on the COST 2100 channel model. This study indicates that it is necessary to optimize the polarization direction of MIMO relay channels.

Multi‐Channel Metasurface for Versatile Wavefront and Polarization Manipulation

AbstractMetasurfaces are extensively studied for the flexible manipulation of wavefront and polarization of electromagnetic waves with significant merits such as ultra‐thin profiles and low insertion losses. However, conventional meta‐devices are usually limited by achieving only single polarization modulation, and it is challenging to achieve mixed polarization and wavefront manipulation in a single metasurface. Here, a single‐layer anisotropic metasurface for independent wavefront manipulation in multiple polarization channels is presented. The meta‐atom is composed of two orthogonal dumbbell‐shaped metal patches placed on the top of a dielectric layer with grounded plane on the bottom. The reflective phases of the two orthogonal linearly polarized waves can be independently manipulated by changing the dimensions of the dumbbell‐shaped resonator. As a result, not only the propagation phase but also the polarization state of the outgoing wave can be manipulated independently as desired. As proof of concept, a metasurface is designed for converging the reflection beams of four polarization states to specific positions for four‐focus holographic imaging. The measured results are in good agreements with simulated ones, verifying the independent wavefront manipulations with arbitrary polarization conversions.

Tree-fruits crop type mapping from Sentinel-1 and Sentinel-2 data integration in Egypt's New Delta project

Horticulture maps are absent in Egypt, despite the vital importance of horticulture crops as a main part of the agriculture economy. The available land use/cover datasets have only one cropland category, with no detailed information on crop types, areas, and spatial distribution, which are essential information for a wide range of agriculture applications. Hence, producing crop type maps from remote sensing was addressed in many studies, focusing more on mapping herbaceous crop types rather than horticulture crops. The earlier studies also indicated the high spectral and phenological similarities among various tree-fruits crops, which hampered the accurate mapping of horticulture crops. Hence, the current study aims to find the best approach for accurate tree-fruits mapping by testing different temporal stacking windows, spectral stacking methods, and various integration scenarios between Sentinel-2 optical (S2) and Sentinel-1 SAR (S1) data as inputs to the random forest (RF) classifier. Comparative accuracy analysis showed that using time series S2 spectral bands (SBs) and vegetation indices (VIs) can classify various tree crop types with very high accuracy (96%), while using S1 polarization channels with some added S1 textural features could yield a high classification accuracy (85.2%). Hence, the optical and SAR data integration further improved the discrimination of tree crops, particularly those with similar spectral characteristics (e.g., mango, citrus, and olive). The use of annual or seasonal time series images achieved better accuracy (by 7–8%) than the monthly stacked images. Despite its high dimensionality, the temporal image that contains all months' S2 SBs & VIs achieved higher accuracy (by 1.5%) than the reduced image that contains the annual statistical layers (e.g., maximum and minimum values of each SBs and VIs). The best integration scenario that achieved the highest accuracy (OA = 96.31 & Kappa = 0.96) was adding S1 textural features to S2 spectral features.