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This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Physics. Please check back later for the full article. The conditions for the Sokolov-Ternov effect to occur are approximately satisfied by electrons (or positrons) circulating on the design orbit of a planar storage ring. Indeed, self-polarization was first observed in the electron/positron colliders Anneau de Collisions d’Orsay (ACO) and VEPP-2. Beam polarization offers an additional tool for understanding the physics events. The possibility of having polarized electron/positron beams for free is therefore appealing. However, the Sokolov-Ternov polarization time constant, proportional to 1/γ5 and to the third power of the bending radius, restricts the region of interest for self-polarization. For the about 100 km Future Circular Collider (FCC) under study at CERN, the polarization constant is about 10 days at 45 GeV beam energy. At high energy the randomization of the particle trajectory due to photon emission in a storage ring with finite alignment precision of the magnets introduces spin diffusion and limits the attainable polarization. In addition, in a collider the force exerted by the counter-rotating particles impact the beam polarization. This force increases with beam intensity and experiments are reluctant to pass up luminosity for polarization. To this day the electron(positron)/proton collider HERA has been the only high energy collider where electron (and positron) self-polarization was an integral part of the physics program.

In this study, we developed a facile method to fabricate three-dimensional (3D) structures composed of FeNi alloy nanoparticles encapsulated in N-doped carbon nanotubes that grafted on the SiO2 spheres (FexNiy@NCNT@SiO2) for electromagnetic wave (EMW) absorption. The experimental results suggest that the impedance matching characteristic can be tuned by the introduction of SiO2 spheres in the 3D structure. Density functional theory (DFT) calculations showed that the introduction of Ni improved the polarization and conductive losses of the FexNiy@NCNT@SiO2. As a result, the optimal 3D structure exhibits excellent EMW absorption property with a reflection loss and effective absorption bandwidth are -49.39 dB and 4.32 GHz, respectively, even though the matching thickness is only 1.6 mm, superior to most magnetic carbon-based composites. Thus, our current approach opens up an effective way to the development of low-cost, high-performance EMW absorbers.

In recent years, the bionic polarized light compass has been widely studied for the unmanned aerial vehicle navigation. However, it is found from the obtained investigation results that a polarized light compass with a sensitive and high dynamic range polarimeter still provides inferior output precision of the heading angle due to the presence of the noise generating from the compass. The noise is existed not only in the angle of the polarization image acquired by polarimeters but also in the output heading data, which leads to a sharp reduction in the accuracy of a polarized light compass. Herein, we present noise analysis and a novel multiscale transform denoising method of a polarized light compass used for the unmanned aerial vehicle navigation. Specifically, a multiscale principle component analysis utilizing one-dimensional image entropy as classification criterion is directly implemented to suppress the noise in the acquired polarization image. Subsequently, a multiscale time–frequency peak filtering method using the sample entropy as classification criterion is applied for the output heading data so as to further increase the heading measurement accuracy from the denoised image above. These two approaches are combined to significantly reduce the heading error affected by different types of noises. Our experimental results indicate the proposed multiscale transform denoising method exhibits high performance in suppressing the noise of a polarized light compass used for the unmanned aerial vehicle navigation compared to existing prior arts.

A miniaturized electrical beam-scanning reflectarray antenna providing a directional beam and wide steering ranges with fixed θ-polarization is proposed. To accomplish these properties, we devise a new active reflectarray cell that can control both the phase and polarization of incident waves. Accordingly, we can enforce all reflected waves to constructively interfere with each other in all target directions. To feed the proposed reflectarray cells, an omnidirectional monopole antenna is installed at the center of the reflectarray, which illuminates the reflectarray evenly. In addition, because the monopole feeder is directly connected to the reflectarray, we can significantly reduce the overall volume of the antenna down to about 0.5 λ3 with a small F/D ratio of 0.147. Consequently, the proposed antenna attains a wide scan coverage and directional beam patterns. Moreover, the antenna can also maintain polarization direction stably, which is strongly required for dynamically moving platforms such as drones and unmanned aerial vehicles (UAVs). The experimental results agree well with the predictions, proving the validity of our approach.

An antenna-in-package (AiP) of end-fire and dual-polarization at 28 GHz is presented. It is formed by four periodic antennas of broad bandwidth and high-isolation, fabricated by the low-temperature co-fired ceramics technology. The dual-polarizations are realized by integrating a horizontal metal stripline-coupled dipole with a vertical magneto-electric monopole, incorporated into a multilayer architecture for compactness. The AiP skillfully implements vertical vias and horizontal strip lines in the cavities between antennas to improve isolation and polarization purity. This AiP has numerically been examined for end-fire high gain and beam steering in user equipment (UE) applications. The prototype was measured to show good isolation lower than -25 dB from 26.5 to 29.5 GHz and agree with full-wave simulations. The antenna array is finally integrated with 1x4 boresight radiation microstrip antennas to form a complete UE AiP.

This paper proposes a design of waveguide slot arrays with asymmetric Iris to achieve broadband properties with high polarization isolation for E-band wireless backhaul systems. The proposed subarray of 2 × 2 radiating slots is excited by two-layered feeding networks carrying two orthogonal waves, and the asymmetric Iris is inserted at the intersection where the waves merge. For verification, a prototype with 16 × 16 radiating slots is fabricated, and its antenna characteristics are measured in an anechoic chamber. The fabricated antenna has a bandwidth of 13 GHz at Port 1 and 10.5 GHz at Port 2 for VSWR ≤ 2.6, and the isolation between two ports is greater than 30 dB within the target frequency bands. The average bore-sight gains of the two ports are 30.85 dBi and 31.67 dBi, and the half-power beam widths are 3.5° and 3.25°. We also fabricate another prototype with 64 × 64 radiating slots for a field test. The proposed prototype is capable of maintaining the received power to be greater than 15 dB for an effective isotropic radiated power of 40.7 dBm at 25 m, which demonstrates that the proposed antenna is suitable to replace current parabolic dish antennas with a reduced profile.

Owing to the complex composition architecture of these solid solutions, some fundamental issues of the classical (1−x)Bi1/2Na1/2TiO-xBi1/2K1/2TiO3 (BNT-xBKT) binary system, such as details of phase evolution and optimal Na/K ratio associated with the highest strain responses, remain unresolved. In this work, we systematically investigated the phase evolution of the BNT-xBKT binary solid solution with x ranging from 0.12 to 0.24 using not only routine X-ray diffraction and weak-signal dielectric characterization, but also temperature-dependent polarization versus electric field (P-E) and current versus electric field (I-E) curves. Our results indicate an optimal Na/K ratio of 81/19 based on high-field polarization and electrostrain characterizations. As the temperature increased above 100 °C, the x = 0.19 composition produces ultrahigh electrostrains (> 0.5%) with high thermal stability. The ultrahigh and stable electrostrains were primarily due to the combined effect of electric-field-induced relaxor-to-ferroelectric phase transition and ferroelectric-to-relaxor diffuse phase transition during heating. More specifically, we revealed the relationship between phase evolution and electrostrain responses based on the characteristic temperatures determined by both weak-field dielectric and high-field ferroelectric/electromechanical property characterizations. This work not only clarifies the phase evolution in BNT-xBKT binary solid solution, but also paves the way for future strain enhancement through doping strategies. © 2021 The Chinese Ceramic Society. This work was supported by the National Natural Science Foundation of China (Grant Nos. 51772239 and 51761145024 ) and the Fundamental Research Funds for the Central Universities ( XJTU ). The SEM work was done at International Center for Dielectric Research (ICDR), Xi'an Jiaotong University, Xi'an, China.

Underwater navigation system is an indispensable part for autonomous underwater vehicles. Due to the indiscernibility of satellite signal, however, the underwater navigation problem is quite challenging, and a satellite-free navigation scheme should be looked for. Polarization navigation, inspired by insects’ capability of autonomous homing and foraging, is an alternative solution to satellite navigation with great application potential. Underwater polarization provides an indirect sun compass to animals for orientation determination. However, it is difficult to apply terrestrial solar-tracking methodologies in underwater situations due to the refraction of polarized skylight at the air–water interface. To resolve this issue, an underwater solar-tracking algorithm is developed based on the underwater refraction-polarization pattern inside the Snell's window. By employing Snell's law and Fresnel refraction formula to decouple the refractive ray bending and polarization deflection, the celestial polarization pattern is obtained based on underwater measurement. To further improve the accuracy, the degree of polarization is employed as a weight factor for E-vector. A long-lasting underwater experiment was conducted to validate the effectiveness of the proposed approach, and the results showed the root-mean-square errors of solar zenith and azimuth employing this algorithm were 0.3° and 1.3°, respectively. Our experimental results show that the refraction-polarization pattern inside the Snell's window exhibits immense potential to improve the solar-tracking accuracy for underwater navigation.

The fabrication of high-performance electromagnetic (EM) wave absorption (EMA) materials is an effective strategy to deal with ever-increasing EM pollution. In this work, a series of manganese oxides/porous carbon (MnxOy@C) hybrid composites are obtained by a two-step process. It is revealed that different manganese oxides play various influence on the dielectric properties of absorbers. Owing to the moderate complex permittivity of MnO@C hybrid composites, the optimal reflection loss could reach as high as -76.0 dB at the matching thickness of 2.0 mm with 5.2 GHz of effective absorption bandwidth at thickness of 2.1 mm. We demonstrated that the addition of porous carbon is vital for enhancing EMA performance of composites, which not only coordinates impedance matching allowing more EM waves enter the absorber, but also provides the path for electron movement, thus profiting conductive loss. Besides, different heterogeneous interfaces including porous carbon, manganese oxide and so on, are conducive to contribution of interface polarization. The most noteworthy is ingenious design of composite materials and systematic research of EM energy attenuation mechanism in this work will provide the possibility to realize high-performance EMA.

Bioinspired polarized skylight navigation, which can be used in unfamiliar territories, is an important alternative autonomous navigation technique in the absence of Global Navigation Satellite System (GNSS). However, the polarization pattern in night environment with noise effects and model uncertainties is a less explored area. Although several decades have passed since the first publication about the polarization of the moonlit night sky, the usefulness of nocturnal polarization navigation is only sporadic in previous researches. This study demonstrates that the nocturnal polarized light is capable of providing accurate and stable navigation information in dim light outdoor environment. Based on the statistical characteristics of Angle of Polarization (AoP) error, a probability density estimation method is proposed for heading determination. To illustrate the application potentials, the simulation and outdoor experiments are performed. Resultingly, the proposed method robustly models the distribution of AoP error and gives accurate heading estimation evaluated by Standard Deviation (STD) which is 0.32° in a clear night sky and 0.47° in a cloudy night sky.

A flexible, dual-broadband and polarization insensitive coding metasurface is proposed to manipulate electromagnetic (EM) scattering in microwave frequency band. The 1-bit coding units “0” and “1” are formed by the Pancharatnam-Berry (PB) phase based on the same-sized meta-atoms with different orientations. The layout of the coding metasurface is obtained through genetic algorithm (GA). The simulation results indicate that the proposed coding metasurface in this paper can achieve more than 10 dB radar cross section (RCS) reduction in the range of 9.26-12.87 and 14.84-19.35 GHz in the planar case, which is attributed to the reorientation of the reflected energies into different directions by optimizing the coding sequence. The diffuse scattering performance in the dual-wideband is well maintained while the coding metasurface is conformal on metallic cylinder with diverse curvature radii. Moreover, the scattering characteristics of conformal metasurfaces become better with the decrease of curvature radius under the case of the certain size of the flexible metasurface. A flexible coding metasurface prototype is prepared and measured. The experiment results coincide with the numerical simulation ones, demonstrating the outstanding capacity of RCS reduction. The proposed design has potential application value in the field of antenna and stealth of more complex objects.

This paper designs a class of low-profile compact MIMO antennas on a single radiating patch using simple and systematic characteristic modes (CMs) method. Rather than using conventional method of radiation pattern and polarization diversities, this work demonstrates that by taking advantage of a proper superposition of some even/odd modes, it is able to generate similar radiation pattern and polarization no matter which port is excited. It is also found that port isolation and impedance matching are dependent on not only operating modes but also input couplings. The proposed CMs method consists of three main steps. First, adjust desired even and odd modes to be equal in resonant frequency (ResF). Second, suppress unwanted modes without affecting desired ones. Lastly, determine feeding positions to obtain proper input couplings. In this way, satisfactory port isolation and impedance matching could be achieved simultaneously and quickly, getting rid of complicated decoupling structures and time-consuming optimization. To exemplify how the proposed CMs method works, two MIMO antennas are successfully designed by just using simple slots and shorting pins. A prototype for the proposed four-port MIMO antenna is fabricated and measured for validation.

This letter presents a reconfigurable antenna that uses gravity to control the self-circulation of liquid metal (LM), thereby realizing an adaptive reconstruction method. Then the polydimethylsiloxane (PDMS) structure with a square ring channel is loaded on the microstrip antenna, and the contact position between the liquid metal and the patch is controlled by gravity, which provides conditions for reconfiguration. The antenna has four reconfigurable frequency bands, which can be switched between the dual circle polarization (left-and right-hand circular polarization) mode and the linear polarization (LP) mode without additional mechanical adjustment structures, radio frequency circuits or related components. The measured results show that the proposed antenna has -10 dB impedance band of 1.2-1.6 GHz, 2.5-2.75 GHz, 4.2-4.55 GHz and 5-5.4 GHz and peak gain of 3.6 dBi, 5.07 dBi, 2.68 dBi and 3.25 dBi within passband, which agree well with the simulated results.

A synthesized strategy for achieving polarization-insensitive metalens is proposed by imposing identical parabolic phase patterns individually on two decoupled left-handed (spin up, σ+) and right-handed (spin down, σ-) circular polarization (CP) channels of an anisotropic scheme. This is enabled by synergizing dynamic phases and local geometric phases within 0° and 90° rotations. As a consequence, similar focusing behavior is expected when it is illuminated by a plane wave of arbitrary polarization since any incoming wave is a superposition of σ+ and σ- wave. Such an intriguing feature can be utilized to engineer a polarization-insensitive reflectarray/transmitarray in a shared aperture by placing a feeding source of different polarizations at its focal spot without altering the array aperture. Therein, the polarization of the meta-array is determined by its feeding which is readily to be changed in practice. For demonstration and possible applications, two reflectarrays composed of 50 × 50 elements at Ku band with one in normal and the other in offset configuration were designed and experimentally characterized. Numerical and experimental results illustrate that both reflectarrays are able to work in dual-linear (LP) and dual CP states by utilizing LP and CP horns of different orientations. Moreover, the versatile polarization-agile property does not pose significant penalty on its radiation performance and both reflectarrays exhibit a measured peak aperture efficiency of 63.8 and 39.6%, respectively near 14 GHz, and a 1dB gain bandwidth more than 11.8 %.

Na0.5(Bi3/4RE1/4)0.5TiO3 (RENBT, RE = Nd, Gd, Dy, and Ho) compounds were investigated in the framework of first-principles calculations using the full potential linearized augmented plane wave (FP-LAPW) method based on the spin-polarized density functional theory implemented in the WIEN2k code. Combined charge density distribution and Ti K-edge X-ray absorption spectra revealed that the RENBT compositions with high polarization values were accompanied by a higher TiO6 distortion, DyNBT, and NdNBT compounds. The effect of the rare-earth elements on the polarization were confirmed experimentally with the collection of the hysteresis loops. The investigation of the electronic properties of the compounds highlighted the emergence of a magnetization owing to the 4f orbital effect of the rare-earth elements. Besides, the investigation of the chemical ordering showed a short-range chemical ordering for the pure composition and an increased A-site disorder for dysprosium doped NBT system. The increased disorder may speak for increased relaxor properties in the RE doped compositions.

Thin film lithium niobate on insulator (LNOI), as an emerging photonic material, provides a promising platform to realize compact, high-speed, and high-efficient electro-optic (EO) modulators. However, due to the large coupling loss caused by the large mode field mismatch between standard single mode fibers and the LNOI waveguides, edge or grating couplers are indispensable to LNOI modulators. In this paper, we propose a novel edge coupler employing staircase structure. The proposed coupler is feasible with i-line lithography and avoids high precise alignment. Moreover, such coupler can be applied to wafer-scale manufacture with low cost. The simulation results show that a low input/output coupling loss of 1.14 dB/1.62 dB can be achieved at 1.55 m wavelength for transverse electric (TE) polarized light signals. Specifically, benefited from the novel staircase design, the proposed edge coupler shows a unique property of polarization extinction ratio larger than 10 dB, which will further improve the modulation efficiency and depth of the EO modulators based on X-cut LNOI.

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 m wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 210-5 to 6.9310-5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 m wavelength.

Considering a series of electromagnetic pollution problems brought by the development of electronic communication technology, more attention has been paid to the research of electromagnetic wave (EMW) absorbing materials with unique composition and structure. Herein, under the inspiration of mixed-dimensional hierarchical structure, 2D Ni2P nanosheets anchored on 1D silk-derived carbon fiber is successfully fabricated as a gratifying resistor-dielectric type absorber. By a controllable pyrolyzation strategy and disproportionated reaction, high-density 2D Ni2P nanosheets were grown vertically and cross-linked on the surface of 1D silk-derived carbon fiber. The sample exhibited superior EMW absorption performance with maximum reflection loss value of – 56.9 dB at the thickness of 2.32 mm and the effective absorption bandwidth can reach to 7.2 GHz at the thickness of 1.93 mm. In addition, the pure Ni2P shows remarkable dielectric characteristic and EMW absorption ability as well. The integration of dual-conductive loss, enhanced polarization relaxation loss and the multiple scattering in the composites was proved to contribute to the good EMW absorption performance. Therefore, this work confirms the great potentials of Ni2P as a high-efficient EMW absorbing materials and light a new way in construction of multidimensional absorber.

High-performance electromagnetic (EM) absorbers are necessary for military and industry application in view of the extensive utilization of EM devices. Carbon fibers (CFs) have been considered as promising candidates in electromagnetic wave (EMW) absorption materials, while the single carbon fiber material cannot achieve satisfactory EMW absorption performance because of its limited impedance matching. Herein, electrodeposition and hydrothermal methods were used to fabricate vertical hollow ZnS nanoarrays on carbon cloth (CC) substrate, and then one kind of novel flexible EM composite absorbers with excellent performance was obtained through adjusting morphology of hollow ZnS nanoarrays by easily changing the synthesis parameters of the precursor. Noteworthy, the miniaturized cone-shaped hollow ZnS nanoarray composite absorber shows excellent EMW absorption performance of strong absorption and wide absorption band. The maximum reflection loss value is −52.5 dB and the effective absorption bandwidth reaches 5.1 GHz when the thickness is only 1.9 mm. At the same time, the composite possesses the characteristics of light weight and thin thickness. The excellent properties of the composite absorbers are mainly attributed to their morphological structure. The unique hollow ZnS nanoarray structure enhances the interface polarization and multiple reflections, meanwhile also giving it the properties of metamaterials with resonant absorption. Furthermore, the adjustment of the ZnS nanoarray morphology can not only change the transmission behavior of EMW but also affect the resonance frequency and intensity of the ZnS nanoarray unit. This study obtains high-performance absorbing materials with flexible characteristics as well as highlights the importance of the adjustment of the morphological structure to improve the EMW absorption performance.

We propose and experimentally demonstrate a polarization-insensitive single sideband modulator based on silicon microring modulators (MRM). The proposed modulator splits and modulates the two orthogonal polarization states of an input laser in a loopback structure, with an on-chip silicon polarization splitter rotator (PSR), overcoming the polarization dependence of the silicon photonic modulator. The IQ configuration of the modulator enables single sideband modulation, thus improving the resistance of the modulated signal to chromatic dispersion and extending the transmission reach. The adoption of an MRM relieves the bandwidth limitation in polarization-diverse versions of SiP Mach-Zehnder modulators (MZM). Our experiments validate the proposed modulator polarization insensitivity and transmission performance.

A cost-effective, conformal, polarization-insensitive, light-weight, ultrathin, and ultrawideband electromagnetic wave absorber covering the entire Ku, K, and Ka bands and the lower V band is presented in this article. The absorber consists of a single layer of inkjet printed resistive metasurface laid over a flexible paper supported by a grounded foam. A novel metasurface pattern is designed by combining a checkerboard inspired symmetrical structure around a central square patch. The notable features of the proposed absorber are its ultrathin thickness of 2.17 mm (0.09 $\boldsymbol{\lambda _l}$ at the lowest operating frequency) for achieving a fractional bandwidth of 117% with a small radar cross section and its suitability for conformal applications. It exhibits more than 90% absorptivity over a frequency range from 11.87 to 45.28 GHz for all the angles of polarization and is also angularly stable. The theoretical, simulation, circuital, and experimental analysis validates the various features exhibited by the absorber.

A method of triple-mode operation by capacitive slot loading is proposed for bandwidth enhancement of single-fed circularly polarized (CP) patch antennas. Instead of using even-numbered linearly polarized (LP) modes with quadrature phase, three orthogonal LP modes are used to CP bandwidth enhancement, where the middle mode is shared by two cross-polarized modes with the same polarization. The advantages include reduced constraints, lower complexity and higher degree of freedom for antenna design. Guided by the method, a U-slot antenna and an E-shaped antenna are proposed and designed with characteristic mode analysis (CMA). Both antennas work with a TM10-like mode and a TM01-like mode. Differently, the U-slot antenna works with an additional slot mode and the E-shaped antenna works with an additional TM11-like mode. The operating modes are manipulated by the slot loadings for creating phase difference. As a result, wideband CP radiation is achieved with single feeding. CMA-based empirical formulas are derived for fast design. The proposed method and antennas are experimentally validated. Both antennas measure a bandwidth exceeding 21% for 10-dB return loss and 3-dB axial-ratio (AR), a significant improvement compared with conventional corner-truncated U-slot patch antennas of similar thickness or volume.

In this paper, an environment-robust polarization-based phase-shift dynamic demodulation method for optical fiber acoustic sensor is proposed. Through optical lever effect of polarization low-coherence interference and amplitude scaling differential cross multiplication (AS-DCM) algorithm, acoustic-source induced interference phase of the acoustic sensor can be demodulated in real-time with high precision. The maximum relative phase demodulation error was only 0.694% when the cavity length had an offset ∼4 μm. The maximum cavity length demodulation error was keeping less than 3.988 nm under the optical power reduced ten times, which demonstrated an ultra-stable demodulation for the largest permitted optical power attenuation range, to our best knowledge. The proposed method has a capability of tolerating large optical power attenuation and large cavity length random offset, providing an environment-robust way for optical fiber acoustic sensor working in extreme environments.

International audience; A 3-in-1 depolarizing circular scatterer for the polarimetric radar calibration is proposed in this paper. The proposed scatterer is low cost, compact, planar circuit, and well suited for the radar operating in a compact range, for example, chipless RFID technology. By the virtue of its circular shape, the rear side of the proposed scatterer acts as a metallic disk with strong co polarization backscattered signals. The front side is composed of eight resonant dipoles which make it nondepolarizing and depolarizing scatterers at the inclination of 0° and 45°, respectively. The features of proposed circular scatterer are tested as reference calibration objects for single antenna based polarimetric radar calibration techniques. Two test objects are utilized: a dihedral tilted at 45° and a depolarizing multi resonant planar structure commonly called chipless RFID tag. The performance of proposed circular scatterer is also compared with the standard reference calibration objects: a metallic disk and a dihedral tilted at 22.5°. The performance of proposed circular scatterer is comparable to the standard reference calibration objects for the calibration techniques (namely Type 1 and Type 2). The proposed scatterer is potentially tolerant of displacement up to 1 cm and misalignment equals 2°.

A circular polarization (CP)-agile and continuous beam-steerable array antenna is presented using a hybrid design approach. It is accomplished by combining digital reconfigurable antenna elements with analog continuously tunable phase shifters. To realize both polarization reconfiguration and initial phase generation for beam-scanning simultaneously, the designed antenna element enables eight states that corresponds to two CP modes with four quantized phases. The phase shifters further provide additional variable phases of -90° to 0° for antenna element excitation. Superposition of the initial and additional phases helps to satisfy a full and continuous 360° phase coverage for a beam-steerable array. Meanwhile, the phase decomposition also facilitates the design of phase shifters without complex or cascaded structures. By altering the bias states of the electronic components loaded in the array antenna, CP switching and beam scanning can be independently controlled. For verification, prototypes of the antenna element, phase shifter, and a four-element array are all fabricated and tested. Reasonable agreement is obtained between simulation and measurement. The resultant array could scan up to nearly ±40° off the boresight, along with stable radiation patterns and good CP performance.

Conventional wisdom says that nonpolar structures do not favorably produce strong second-harmonic generation (SHG) responses since the polarization in their microscopic functional groups are counte...

A decoupling structure with polarization rotation property (DSPR) is proposed to reduce the mutual coupling between co- or cross-polarized antennas. The proposed DSPR generates a neutralization wave with two orthogonally polarized components that can be controlled to cancel the original mutual coupling. The DSPR is placed above the arrays with orthogonal and parallel dipole elements. After applying the DSPR, the mutual coupling at the center frequency of 3.5 GHz is reduced to -40 dB for both arrays, and the overall mutual coupling is better than -26 dB within the band of 3.3-3.7 GHz, and the reflection coefficients remain below -12 dB. The antennas maintain stable radiation patterns within the operation bandwidth with a 0.5-dB increase of the realized gain. Since the DSPR can effectively reduce both co- and cross-polarization coupling, the mutual coupling between circularly polarized antennas in a 1×4 array is reduced to below -35 dB thanks to the DSPR. Finally, a prototype of the antenna array with orthogonal dipole elements loaded with the DSPR is fabricated and measured. The measured results are in excellent agreement with the simulated ones, demonstrating the effectiveness of the proposed DSPR for isolation enhancement between cross-polarized antennas.

Indium gallium nitride (InGaN) vertical-cavity surface-emitting lasers (VCSELs) with top dielectric and bottom pipe-gallium nitride (GaN) distributed Bragg reflectors (DBRs) were demonstrated. Pipe-GaN DBR structure consisted of a lateral wet-etched pipe-GaN layer and a GaN layer in the 20 pair stack structure as an embedded reflector. The optical birefringence behavior of the anisotropic pipe-GaN structure induced the polarization properties in the reflectance and electroluminescence (EL) spectra. Polarization EL emission peaks with narrow line-widths were measured at 430.8 nm (perpendicular to pipe-GaN) and 432.5 nm (along with pipe-GaN), respectively. The EL emission peaks with high polarization ratios were observed due to the short resonance cavity effect with the birefringence pipe-GaN DBR structure.

Because of the anisotropy of snow surface reflectance, it is essential to select a proper snow bidirectional reflectance model for extracting snow cover and inverting snow properties from remote sensing image, especially during the period of snow rapidly changed. In this letter, the ability of reproducing snow bidirectional reflectance by three semiempirical bidirectional reflectance distribution function (BRDF) models (Ross-Li, Roujean, and Raman-Pinty-Verstraete) and the asymptotic radiative transfer theory (ART) model was evaluated using the polarization and directionality of the earth reflectance (POLDER) data. In addition, the ART model was compared with the bicontinuous geometric optics (bic-GORT) model based on field measurements. The results indicated that the root mean square errors (RMSEs) are small and similar for all models during the stable-snow period. The physical models perform better than the semiempirical models in capturing the bidirectional signatures of snow during the periods of snow rapidly changed. The bic-GORT model achieves higher accuracy, while the ART model holds the advantages of simple and efficient to be used.

This paper comprehensively investigated noise characteristics of superluminal propagation based on low-noise single-frequency Brillouin lasing oscillation with the aid of a population inversion dynamic grating. Thanks to high-degree polarization alignment between the Brillouin pump and the lased Stokes lightwaves in polarization maintaining fibers, efficient Brillouin lasing resonance with over 10-dB relative intensity noise suppression has been demonstrated to activate Brillouin loss-induced anomalous dispersion in the vicinity of pump signals, benefiting a noise-insensitive superluminal propagation along kilometer-long optical fibers with robust resistance to ambient disturbance. Consequently, sinusoidally modulated pump signals experienced the time advancement of 4634.0 ns at the group velocity of 10.63c. Results show that the variance of the fractional advancement with polarization maintaining fibers is 2.54 × 10−4 which is two orders of magnitude lower than that of conventional single mode fibers. Furthermore, the dependence of the group velocity on the modulation frequency was experimentally investigated, showing good agreement with the theoretical analysis.

Image taken in turbid media generally exists poor visibility and low contrast, which results from attenuation of the propagated light. In this letter, an effective polarization-based image dehazing method is proposed, which relies on the relationship between the angle of polarization (AoP) from the Stokes vector and the scattered light. To avoid the influence of noise, AoP is optimized based on regularization constraints. The regularization function is made using an assumption that adjacent pixels with similar colors have similar values of AoP. Moreover, according to the revised AoP information, all the key parameters can be effectively and automatically estimated without considering the no-object region (or the sky region) exists or not, which relies on a frequency prior strategy. Extensive experiments on real-world images demonstrate that the proposed method is more effective than several previous image restoration or enhancement works.

Optical remote sensing is one of the most popular methods for estimating leaf nitrogen concentration (LNC). This nondestructive approach based on reflected intensity measurements has been applied to estimate the variation and distribution of nitrogen concentration in leaf and canopy levels in numerous studies. However, both intensity and polarization are necessary to describe the optical properties of light reflected from leaves and to estimate LNC estimation. In this study, based on the Stokes parameters, the total reflectance, the polarized reflectance, and the nonpolarized reflectance factors (NpRFs) were simultaneously obtained through polarimetric hyperspectral measurements under varied source-viewing geometries in both laboratory and field conditions. Several published hyperspectral indices based on the NpRF showed much better LNC estimation accuracy than those using the total reflectance factor. A clear improvement was found in the viewing directions dominated by specular reflection. Thus, using multi-angular polarimetric hyperspectral measurements not only improves the accuracy of hyperspectral indices on LNC estimation using the NpRF, but also enables the hyperspectral indices to be effective for a wide range of viewing angles. Moreover, polarimetric measurements deepen the understanding of the optical properties of light reflected from leaves. These results indicate that the combination of multiangular, polarimetric, and hyperspectral measurements may play a key role in the estimation of LNC.

This letter proposes a squeeze-and-excitation Laplacian pyramid network with dual-polarization feature fusion (SE-LPN-DPFF) for ship classification in synthetic aperture radar (SAR) images. SE-LPN-DPFF offers three contributions – 1) dual-polarization (VV and VH) feature fusion (DPFF), 2) channel modeling by the squeeze-and-excitation (SE) to balance each polarization feature’s contribution, and 3) Laplacian pyramid network (LPN) to achieve multi-resolution analysis (MRA). Extensive ablation studies can confirm the effectiveness of each contribution. Results on the three- and six-category OpenSARShip datasets reveal the state-of-the-art SAR ship classification performance.

In this article, a novel 1.05-1.25 GHz filtering antenna feeding network with reconfigurable frequency and polarization is proposed. It simply consists of a reconfigurable in-/out-of-phase filtering power divider (RFPD) and a 90° hybrid coupler. By controlling the varactors in the RFPD without any switch component, the proposed 3-port feeding network offers continuous reconfigurable filtering responses with four switchable output patterns including: equal power dividing with phase difference of negative or positive 90°, single-ended output at either output port. With this proposed feeding network connecting to a regular dual-polarized antenna, the resulted antenna system can easily realize reconfigurable polarization of vertical polarization (V-LP), horizontal polarization(H-LP), left-handed circularly polarization (LHCP) and right-handed circularly polarization (RHCP), in addition to its reconfigurable filtering responses. A prototype using microstrip technology is designed, fabricated and measured to demonstrate the proposed technique. Good agreement between simulated and measured results is obtained. The measured results show that the feeding network covers a frequency range of 1.05-1.25 GHz, and the error of phase difference and amplitude imbalance are less than 5° and 0.5 dB, respectively. The resulted antenna beams can be freely switched in four polarization states with good performance.

Active and passive microwave characteristics of diurnal soil freeze-thaw transitions and their relationships are crucial for developing retrieval algorithms of the soil liquid water content (θliq) and freeze/thaw state, which, however, have been less explored. This study investigates these microwave characteristics and relationships via analysis of ground-based measurements of brightness temperature (TB) and backscattering coefficients (σ⁰) in combination with simulations performed with the Tor Vergata discrete radiative transfer model. Both an L-band (1.4 GHz) radiometer ELBARA-III and a wide-band (1-10 GHz) scatterometer are installed in a seasonally frozen Tibetan meadow ecosystem to measure diurnal variations of TB and copolarized σ⁰ at both hh (σhh⁰) and vv (σ vv⁰) polarizations. Analysis of measurements collected between December 2017 and March 2018 shows that 1) diurnal cycles are observed in both TB and σ ⁰ due to the change in surface θliq caused by diurnal soil freeze-thaw transitions; 2) a negatively linear relationship is found between e and σ⁰ regardless of frequency, polarization combinations, and observation angles; 3) slopes (β ) of linearly fit equations between eH and σhh⁰ decrease with increasing observation angles of ELBARA-III, while the ones between eV and σvv⁰ increase with increasing observation angles; and 4) correlations between e and σ⁰ increase with decreasing microwave frequency of σ⁰ measurements and ELBARA-III observation angles, and magnitudes of diurnal σ⁰ cycles also increase with decreasing microwave frequency. Moreover, the calibrated Tor Vergata model shows capability to reproduce both diurnal e and σ⁰ variations as well as to quantify their relationships at different frequencies and observation angles.

A simple optically transparent absorber based on a double complementary structured layer of indium tin oxide (ITO) deposited polyethylene terephthalate (PET) film is presented. The structure showed more than 90% absorption from 2-4.5 GHz of the frequency with a thickness of 0.0847L (wavelength corresponding to the lowest frequency of absorption band). The computed absorptivity of the proposed structure is validated using the transmission line theory and measured experimentally as well. The structure has polarization insensitive response and is highly stable for oblique wave incidence over a wide angular range. This absorber can be conformally wrapped on a curved surface and reduces the radar cross-section (RCS) by more than 10 dB of a curve cylinder. This 10 dB RCS reduction covers almost the entire S-band of microwave frequencies. Optical transparency and flexibility of the proposed absorber make it suitable for a wide range of applications.

Calculations involving polarization propagation in dielectric media require the adoption of various, often unstated, conventions, an important one of which is the sign of the complex argument ±i(ωt - βz). In this paper we show that the form of the dielectric tensor and, hence, the forms of both the Jones and Stokes representations of states, operators, and transformations depend on that sign choice. We show that, while physical observables cannot depend on the choice of convention, errors and ambiguities can occur if adherence to the various conventions is not followed consistently. By methodically developing polarization propagation in both sign conventions we provide a means for unambiguous comparison of results from analyses that employ different, sometimes mixed, conventions. We also include conventions such as assignment of Pauli matrices to Stokes axes and choice of chirality for circular polarizations.

Understanding the optical properties of light reflected from snow surfaces is fundamental for remote sensing-based characterizations of snow properties and quantification of radiative transfer in the atmosphere-earth system. In theory, both intensity and polarization are required for describing the optical properties of light reflected from snow. However, thus far, a few studies have focused on the polarimetric properties of snow. In this study, we measured both multiangular photometric and polarimetric (based on the Stokes parameters) hyperspectral field results of snow with different properties (grain size, pollution levels, and microscopic surface roughness). By considering the absorption ratio of the polarizer, the intensity defined by photometric results [bidirectional reflectance factor (BRF) and hemispherical directional reflectance factor (HDRF)] was first confirmed to be similar to those derived from polarimetric measurements [I parameter reflectance factor (IpRF)] of snow surfaces. Then, the bidirectional polarized reflectance factor (BPRF) of snow, which is used to define the polarimetric properties of snow, was found to be useful for characterizing snow properties. Moreover, comparing ground measurements of snow BPRF with modeled results, we found that some existing BPRF models did not match well with the BPRF measured in the 2π space. These results suggest that more attention should be paid to the combination of IpRF (BRF or HDRF) and BPRF because polarimetric measurements can be used both for describing the optical properties of light reflected from snow and for quantifying snow properties.

This paper presents a very thin metasurface (MS) planar lens for millimeter wave MIMO applications. The MS planar lens consists of array of mm-wave resonators providing varying phase response to transform the phase profile of the electromagnetic wave propagating through this array. Each resonator consists of two identical layers having substrate separated by an air gap of h=0.8mm and are 4mm × 4mm in size. The MS lens having a focal length of f=12mm is loaded to a three-port proximity fed antenna array to operate at 27.5 GHz to 32 GHz. the designed lens is polarization insensitive and can be used with any polarization. The three-port antennas with the MS lens is fabricated and tested, measured results have confirmed a beam scanning of ± 15° with a peak gain of 20.2dBi for port-2.

Terahertz (THz) technology offers multifaceted capabilities and disruptive applications in line-of-sight wireless communication, highly sensitive (bio)sensing, imaging and so on. However, the severe lack of polarization devices comparable to those for other electromagnetic frequencies is impeding moving towards practical applications. Here we demonstrate, for the first time, silicon-based integrated, high polarization extinction ratio, low insertion loss, and compact THz polarization beam splitters (PBSs) fabricated by CMOS-compatible technologies based on dielectric environment variation induced evanescent wave coupling effect. Through comprehensively analyzing working principles of conventional two-waveguide-based PBS, a high-performance three-waveguide PBS is successfully realized. Further optimizing the device parameters and working bandwidth, we achieve an integrated broadband PBS based on cascaded asymmetric directional couplers, whose polarization extinction ratios reach up to 20 dB and 32 dB for transverse electric and transverse magnetic modes, respectively, and their 10-dB bandwidth is 32 GHz for a device length of 15.5 mm. These numbers are the highest in silicon-based integrated THz PBSs so far. We believe our observations provide an effective way for exploring on-chip high-performance THz-PBSs for polarization-diverse systems, accelerating the development and application of on-chip THz photonics.

Reconfigurable intelligent surface (RIS) has drawn worldwide attention because of its attractive capability to improve the electromagnetic propagation environment and surprising advantages of low cost and low power consumption. Recently, RIS is further advanced to realize the independent control of two orthogonal polarizations in real time. In this paper, we study the dual-polarized RIS-assisted mobile communication system and investigate its performance under practical polarization imperfections. Specifically, we provide a tight upper bound of the ergodic spectrum efficiency. Through the bound, we find that the performance is greatly dependent on the polarization imperfections and RIS phase shifts of the RIS-assisted link, when the number of base station antennas is large enough and the deterministic component exists in the RIS-assisted link. On basis of this tight bound, we propose an approximate optimal RIS phase shift design to maximize the ergodic spectrum efficiency upper bound and emphasize the necessity to make phase adjustment between two polarizations of the RIS. Theoretical analysis further gives guidance for the configuration of RIS. Numerical results demonstrate that the upper bound is very tight and the proposed phase shift design with adjustment is approximate optimal.

One of the challenges in ocean surface current retrieval from synthetic aperture radar (SAR) data is the estimation and removal of the wave-induced Doppler centroid (DC). This article demonstrates empirically the relationship between the dc derived from spaceborne X-band InSAR data and the ocean surface wind and waves. In this study, we analyzed over 300 TanDEM-X image pairs. It is found that the general characteristics of the estimated dc follow the theoretically expected variation with incidence angle, wind speed, and wind direction. An empirical geophysical model function (GMF) is fit to the estimated dc and compared to existing models and previous experiments. Our GMF is in good agreement (within 0.2 m/s) with other models and data sets. It is found that the wind-induced Doppler velocity contributes to the total Doppler velocity with about 15% of the radial wind speed. This is much larger than the sum of the contributions from the Bragg waves (~0.2 m/s) and the wind-induced drift current (~3% of wind speed). This indicates a significant (dominant) contribution of the long wind waves to the SAR dc. Moreover, analysis of dual-polarized data shows that the backscatter polarization ratio (PR=σ⁰VV/σ⁰HH) and the dc polarization difference (PD=|dcVV|-|dcHH|) are systematically larger than 1 and smaller than 0 Hz, respectively, and both increase in magnitude with incidence angle. The estimated PR and PD are compared to other theoretical and empirical models. The Bragg scattering theory-based (pure Bragg and composite surface) models overestimate both PR and PD, suggesting that other scattering mechanisms, e.g., wave breaking, are involved. In general, it is found that empirical models are more consistent with both backscatter and Doppler data than theory-based models. This motivates a further improvement of SAR dc GMFs.

A simple and multi-layer metamaterial made of graphene to realize excellent manipulation of EIT-like effect is proposed. The unit cell consists of four layers: Substrate 1, Cross 1, Substrate 2 and Cross 2, which can obtain tunable EIT-like effect by adjusting the Fermi level of graphene. The surface current distributions of four different views clearly explain the underlying physical mechanism. A three-level Λ-type system is employed to describe the coupling process between Cross 1 and 2. The calculated transmission spectra based on two-particle model have great agreement with the simulated transmission spectra. In addition, the effects of geometrical parameters on EIT-like effect are discussed and wideband EIT-like effect with high transmission can be obtained by adjusting the lengths of Cross 1 and 2. Also, the polarization-insensitive character of EIT-like metamaterial is confirmed by the transmission spectra under different polarization angles. The maximum of group delay (25.48 ps) is far greater than the group delay of previously reported EIT-like metamaterials. Our study provides a novel way for the development of slow-light devices and modulators.

The conductive networks for electron hopping and migration constructed by one-dimensional (1D) composite absorbers are highly desirable to improve the electromagnetic (EM) wave attenuation capacity. Herein, the Ni@Co/C@polypyrrole (PPy) composites integrating the advantages of component and microstructure were fabricated. The addition of Co/C and PPy effectively optimized the impedance matching and improved the EM attenuation. Under the comprehensive impacts of multiple reflections/scattering, conduction loss and interface polarization, the Ni@Co/C@PPy composites showed superior EM wave absorption with the reflection loss (RL) value of −48.76 dB and the effective absorption bandwidth (EAB) of 5.10 GHz at a corresponding thickness of 2.0 mm. The largest EAB could reach 5.54 GHz (7.24–12.78 GHz) at the thickness of 2.2 mm. This work provides a great reference for fabricating 1D novel EM wave absorption materials.