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In this communication, we develop and experimentally test a fully tunable magnet-free, non-reciprocal, split-ring resonator-based metamaterial. Non-reciprocity in the material response is introduced by bridging the split-ring gap with a biased field-effect transistor (FET) transistor, which allows the non-reciprocity to be tuned with respect to gate–source and drain–source bias conditions. As a measure of non-reciprocity, we consider the Faraday rotation of a normally incident linearly polarized planewave, which is a function of the co-polarized and cross-polarized $S$ -parameters associated with two horn antennas that transmit and receive the wave. Faraday rotation is calculated with respect to the operating frequency of the horn antennas and manually measured with respect to drain–source current at the resonant frequency. Interestingly, we find a linear relationship between Faraday rotation and drain–source current at the resonance. [ABSTRACT FROM AUTHOR]

Ionospheric Faraday rotation distorts satellite radar observations of the Earth’s surface. While its impact on radiometric observables is well understood, the errors in repeat-pass interferometric synthetic aperture radar (InSAR) observations and hence in deformation analysis are largely unknown. Because Faraday rotation cannot rigorously be compensated for in nonquad-pol systems, it is imperative to determine the magnitude and nature of the deformation errors. Focusing on distributed targets at L-band, we assess the errors for a range of land covers using airborne observations with simulated Faraday rotation. We find that the deformation error may reach 2 mm in the copol channels over a solar cycle. It can exceed 5 mm for intense solar maxima. The cross-pol channel is more susceptible to severe errors. We identify the leakage of polarimetric phase contributions into the interferometric phase as a dominant error source. The polarimetric scattering characteristics induce a systematic dependence of the Faraday-induced deformation errors on land cover and topography. Also, their temporal characteristics, with pronounced seasonal and quasi-decadal variability, predispose these systematic errors to be misinterpreted as deformation. While the relatively small magnitude of 1–2 mm is of limited concern in many applications, the persistence on semiannual to multiannual time scales compels attention when long-term deformation is to be estimated with millimetric accuracy. Phase errors induced by uncompensated Faraday rotation constitute a nonnegligible source of bias in interferometric deformation measurements. [ABSTRACT FROM AUTHOR]

Faraday isolator with composite terbium gallium garnet TGG/sapphire magneto-optical elements that were produced by the surface-activated direct bonding method was created. Thermally induced depolarization and thermal lens for composite elements were investigated experimentally and numerically. The resulting structures operated successfully at a high radiation power, providing an isolation ratio exceeding the classical single element made of TGG by 5 dB and amounted to 34 dB at a laser power of 700 W. The maximum operating power at which the isolation ratio was higher than 30 dB was estimated to be over 2 kW, which is almost 3 times more than in the case of a single TGG. [ABSTRACT FROM AUTHOR]

The radiometer on the NASA Soil Moisture Active/Passive (SMAP) mission is a fully polarimetric instrument that operates at L-band in the spectrum window at 1400–1427 MHz protected for passive use only. A unique feature of the radiometer is the fully digital back-end which permits direct computation of the third and fourth Stokes parameters: the real and imaginary part of the correlation of signal at horizontal and vertical polarizations, respectively. In particular, the SMAP conical scanning geometry provides the opportunity to look at the global distribution of the fourth Stokes parameter, TA4, at constant incidence angle (40°). A striking feature of TA4 is the existence of a strong (±10 K) spurious signal at coastlines. This article provides examples of the spikes and an explanation of the cause. Simulations have shown that the spurious signal is associated with antenna imperfections, such as cross polarization coupling and phase mismatch between polarizations. [ABSTRACT FROM AUTHOR]

According to Faraday rotation effect and Fresnel reflection theory, a novel magnetic field intensity sensor is theoretically proposed and experimentally demonstrated by introducing a 6.4-cm-long tellurite (76.5TeO2-6BiO3-11.5Li2O-6ZnO) no core fiber (TBLZ NCF) into the loop of Sagnac interferometer. The large Verdet constant of TBLZ NCF will bring about an apparent Faraday rotation angle in magnetic field sensing, and the large refractive index difference between TBLZ and silica fibers makes the Fresnel reflection more obvious. The designed sensor demonstrates a sensitivity of 13.51 pm/Gs with an accuracy of 1.47 Gs in the measuring range of 0–380 Gs. It has satisfactory linearity, repeatability, and stability, and does not require additional utilization of expensive magnetic field sensitive materials, exhibiting great application potential. [ABSTRACT FROM AUTHOR]

A discontinuous Galerkin time-domain (DGTD) method based on the current density equation in a 3-D case is proposed for the simulation of electromagnetic (EM) waves in magnetized plasma. In this article, two paths are given for the derivation of time-domain iteration formulas, auxiliary differential equation method for the current density equation (ADE-JE) and LT-JE. The implementation is explained in detail. The proposed algorithm avoids additional data storage and has a relatively high calculation speed, which makes it a powerful tool for magnetized plasma. The algorithm is validated by numerical examples, such as the Faraday rotation effect test and time-varying example. [ABSTRACT FROM AUTHOR]

We demonstrate the detection of phase-resolved magnetization dynamics with combinatorial magneto-optic Kerr and Faraday effects. The method uses a continuous-wave laser that is amplitude-modulated at the spin dynamic frequencies and thus allows for coherent tracking of the spin dynamics, akin a “lock-in”-type measurement. In particular, our method, using a single 1550 nm wavelength, probes simultaneously the ferromagnetic (FM) resonance of Y3Fe5O12 (YIG) and Permalloy (Py = Ni80Fe20) in a YIG-Py heterostructure. The fiber-based magneto-optic components also have the advantage of being made into a compact, tabletop or even portable system with yet robust measurement performances. We believe that our method will be found useful in studying hybrid quantum magnonic systems and/or investigating phase-resolved spin dynamics in nanomagnet structures involving both FM insulators and metals. [ABSTRACT FROM AUTHOR]

Magnetic field monitoring devices are essential for studying and operating high-temperature superconducting (HTS) magnets. Apart from conventional Hall sensor, passive optical fiber sensor is also an option for magnetic field monitoring. In this article, we proposed a novel access based on yttrium iron garnet magneto-optic (YM) sensor, which is one kind of optical fiber sensors, to measure magnetic fields generated by an HTS double pancake coil. Moreover, we used a magnetic field bypass tube made of silicon steel material to expand the measurement range of YM sensor. The test results of YM sensor in liquid nitrogen demonstrated that the YM sensor was benchmarked against Hall probe up to 24.7 mT at 77 K. Using a silicon steel tube to shield magnetic field could extend the field measurement range to 37.6 mT. YM sensor could be one of the promising methods for monitoring HTS magnet magnetic field. [ABSTRACT FROM AUTHOR]

We describe a charge detector that utilizes a high-gain, differential solid-state amplifier with active reset and a novel technique to measure the gain using a custom optoelectronic system. Implemented in a 180-nm complementary metal–oxide–semiconductor (CMOS) process, the amplifier realizes a high gain of $8.9~\mu \text{V}/\text{e}-$ and single-pass rms noise of 475e− for 10-ms time interval with a 300-kHz low-pass filter corner. Operating at a sampling frequency of 10 kHz, the active reset extends the dynamic range of the detector. The amplifier is the first instance of a charge detector that combines a differential topology, active reset, and small feedback capacitors for low-noise, high-gain, high-dynamic-range, and robust operations. The proposed optoelectronic test system injects an adjustable input photocurrent as low as 33 pA to precisely quantify the detector’s gain without the need for a known calibration capacitance. The amplifier is directly wire-bonded to a PCB that has a built-in 1-cm2 Faraday cup. The gain and noise performance have been characterized for a range of input capacitance, and the results show good agreement with simulations. The test system additionally demonstrates the ability to inject a time-varying input at the picoamphere levels to characterize the dynamic response of the detector. An electrospray system confirms that the detector responds to free-space charge and that it can process an input as large as 56 000e− without saturation. The compact and high sensitivity design qualify the device for use in charge detection applications, such as mass spectrometry and space instruments. [ABSTRACT FROM AUTHOR]

Compact-hybrid SAR (CP) is a dual-polarization (dual-pol) SAR mode that transmits a circular polarization (CirP) and measures the received signal at the horizontal and vertical antenna polarization. It is now admitted that the actual SAR technology does not permit the generation of a perfectly CirP and this may significantly affect CP radiometric and phase information. Since all the existing CP calibration models assume a perfectly transmitted CirP, there is an immediate need for the development of a new model that permits efficient assessment and calibration of CP non-circularity. In this article, a new general polarimetric hybrid SAR model (PolHyb) is introduced for both dual- (CP) and quad-polarization hybrid SAR modes. PolHyb explicitly includes the transmitted polarization non-circularity, in addition to conventional radar transmit and receive distortion matrices, channel imbalances and Faraday rotation contamination. The non-circularity of transmitted polarization is expressed in terms of the axial ratio (AR), which used to be popular in the 1960s for characterization of circularly polarized (transmit and receive) dual- and quad-polarization radar. The new CP model derived from PolHyb is adapted to PALSAR2-CP and used as the basis of an efficient method for an assessment of CP non-circularity using Amazonian rainforests. PALSAR2-CP data collected at four different beams (H2–6 to H2–9), with incidence angle varying between 30° and 45°, allows for the first ever demonstration of non-circularity of PALSAR2 CP transmitted polarization. Although it is lower than 0.5 dB for H2–6 and H2–7, the AR of PALSAR2-CP transmitted polarization increases significantly with incidence angle to reach up to 1 dB at Beam H2–8, and 2.3 dB at the highest incidence angles of Beam H2–9. [ABSTRACT FROM AUTHOR]

Fiber-optic magnetic field sensors are attracting interest for applications in navigation, magnetic resonance, geophysics, space systems, power transformers, and generators, especially for harsh environments, at long distances, and for multiple monitoring points. This article presents a computational modeling for optical fiber-based magnetic field sensors using the magnetooptical Faraday and Kerr effects on the polar configuration. We propose two sensor profiles: one using a thin film of Fe and the other using a Ce:YIG layer. A simplified analytical model based on Fresnel equations is used to guide the numerical modeling built on COMSOL Multiphysics. The sensors’ design methodology is also presented, which optimizes the sensor operating range and sensitivity. The proposed sensor sensitivity, resolution, and operating range are presented and compared to others found in the literature. The results indicate the possibility of building high-resolution sensors for a restricted range of magnetic field intensities or a wide-operating range sensor. [ABSTRACT FROM AUTHOR]

The expressions for the thermal lens of linearly polarized radiation arising in m3m, 432 and $\bar {4}3\text{m}$ cubic crystals with arbitrary crystallographic axes orientation in the presence of circular birefringence $\delta _{\mathbf {c}}$ are analyzed. It is shown that the thermal lens may have astigmatism the magnitude of which is proportional to the power of heat generation. The Euler angles determining the crystallographic axes orientation [P] are found and the conditions for the material constant – optical anisotropy parameter $\xi $ – under which the thermal lens astigmatism in active and magneto-active optical elements can be eliminated, are formulated. It is demonstrated that the orientation [P] depends only on optical anisotropy parameter $\xi $ of the crystal and on circular birefringence $\delta _{\mathbf {c}}$. [ABSTRACT FROM AUTHOR]

A capacitive impedance metasurface combined with a transceiver coil to improve the radio frequency magnetic field for 1.5T magnetic resonance imaging applications is presented. The novel transceiver provides localized enhancement in magnetic flux density when compared to a transceiver coil alone by incorporating an electrically small metasurface using an interdigital capacitance approach. Full field simulations employing the metasurface show a significant improvement in magnetic flux density inside a homogeneous dielectric phantom, which is also shown to perform well for a range of depths into the phantom. The concept was experimentally demonstrated through vector network analyzer measurements and images have been taken using a 1.5T MRI scanner. The results show there is a 216% improvement in transmission efficiency, a 133% improvement in receiver signal-to-noise-ratio (SNR), and a 415% improvement in transceiver SNR for a particular transmission power when compared against a surface coil positioned at the same distance from the phantom, where these improvements are the maximum observed during experiments. [ABSTRACT FROM AUTHOR]

We present a new low-profile, wideband, transmitarray design based on polarization-rotating (PR), miniaturized-element, frequency-selective surfaces (MEFSSs). These MEFSS unit cells rotate the polarization of the transmitted wave by 90° either in the counterclockwise or in the clockwise direction. Each PR element consists of three metal layers separated by two dielectric substrates. The constituent metallic layers comprise metallic strips with specific alignments to twist the polarization of the transmitted electromagnetic wave by ±90°. We used the two rotation directions to achieve a 0°/180° phase difference in the transmission mode to achieve a 1 bit phase shifter. We also show that variations in the unit cell dimensions can be combined with polarization rotation to create an additional 90° phase shifts, which can be combined with the PR phase shift mechanism to achieve a 2 bit phase shifter. We designed, fabricated, and experimentally characterized two illustrative transmitarray prototypes with 1 and 2 bit phase-correction patterns. The measured results agree well with the simulation predictions and demonstrate wideband operation for both arrays. The measured 3 dB gain bandwidth and maximum gain are 33.4% and 24.5 dBi, respectively, for the 1 bit prototype, and 24.1% and 27.2 dBi, respectively, for the 2 bit prototype. [ABSTRACT FROM AUTHOR]

Low-frequency synthetic aperture radar (SAR) sensors are prone to ionospheric irregularity structures that affect the amplitude and/or phase of the radar signal. Azimuthal striping caused by amplitude scintillation in SAR data is an initial observation of such effects. In the absence of any physical model and/or technique to mitigate scintillation stripes, we have applied a 2-D fast Fourier transform (FFT) approach for improved interpretation and target identification in fully polarimetric SAR (POLSAR) model-based decomposition scattering powers. Few scenes of fully polarimetric Advanced Land Observation Satellite-Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR) and ALOS-2/PALSAR-2 under different ionospheric conditions are acquired and used in this study. As a reference, data sets over the same areas are also acquired on different dates with negligible ionospheric activity (ionospheric quiet day). All the data sets are corrected for the Faraday rotation angle ($\Omega$), which is estimated using the Bickel–Bates approach. Three correction strategies of scintillation-affected model-based scattering power decomposition images are presented. The strategies (zero masking, thresholding, and averaging-post-thresholding) are implemented on 2-D FFT of scattering power images. An intercomparison of corrected decomposition results from the correction strategies demonstrates the capability of 2-D-FFT-based correction strategies to improve the dominant scattering component by 3%–5% for homogeneous terrains. The correction method based on averaging-post-thresholding gives the best results that are further tested by performing a supervised classification. The overall accuracy and kappa coefficient (${OA}, \hat {k}$) of the averaging-post-thresholding technique (72.87%, 0.59) is comparable to those of the reference data (78.74%, 0.69). [ABSTRACT FROM AUTHOR]

Magnetoresistive sensors combined with permanent magnets are becoming increasingly popular for measuring mechanical displacement and motion in industrial, automotive, and consumer applications. For measurement of rotation, 360° angle sensors are often implemented with giant magnetoresistance or tunneling magnetoresistance sensing elements. These magnetoresistive sensors require the use of an antiferromagnet/ferromagnetic pinned layer (PL), and the finite value of the pinning field of these PL structures limits the operating magnetic field range of the sensor due to slight movement of the PL magnetization induced by the component of magnetic field from the rotating permanent magnet that is orthogonal to the PL magnetization direction. This effect shows up as a distortion of the output waveform of the sensor and increased angle measurement error. This limit on magnetic field dynamic range decreases magnet-to-sensor air gap tolerance and makes the sensors more susceptible to error resulting from external magnetic field exposure. In order to solve this problem, a novel magnetic angle sensor design that includes a round ferromagnetic attenuator placed over each magnetoresistive sensing element within the magnetic angle sensor chip was devised. This design has been tested and shown to increase the upper limit of the magnetic field operating range from 200 Oe to over 1 kOe. [ABSTRACT FROM AUTHOR]

Samples of TAG ceramics doped with Ce and Pr ions (0, 0.5, 1, 1.5, 2 at.% concentrations) and with Ho ions (0.5 at.%) were studied. The wavelength dependence of the Verdet constant of each sample in the 405 nm – 1064 nm range was measured, and analytical approximation was found. The obtained value of the Verdet constant of the studied TAG ceramics did not depend on the dopant concentration and type in the studied range of concentrations. The dependence of thermally induced depolarization on laser radiation power was investigated, and the magneto - optical figure of merit was estimated for each studied sample. It was demonstrated that doping of ceramics can provide a substantial reduction of the magneto-optical figure of merit. The obtained results will be useful for creating Faraday isolators and rotators based on TAG ceramics. [ABSTRACT FROM AUTHOR]

The utilization of a bismuth-substituted iron garnet as a magnetooptic Faraday rotator (MOFR) has been reported for all-optical networking purposes as well as for other applications. Our measurements and observations demonstrate that the MOFR saturates once a significantly large magnetic field (>225 G) is applied. After the applied magnetic field enters the saturation region, the material’s magnetic domains can become pinned at intermediate levels of magnetization. Pinning in this form has not been reported nor well studied for this application. In this paper, a method to detect and describe anomalous pinning in terms of Faraday rotation is presented. Measurements on the changes in the state of polarization that a pinned material produces are examined. This paper will also present practical methods for unpinning the MOFR material, which are traditionally considered to be challenging. [ABSTRACT FROM AUTHOR]

The control of the magnetization at the microscale by pure optical means is fundamentally interesting and promises faster speeds for data storage devices. Although several experiments have shown that it is possible to locally reverse the magnetization of a ferromagnetic system by means of laser pulses, a completely theoretical description of these all-optical switching (AOS) processes is still lacking. Here, we develop an advanced micromagnetic solver that is applied to the numerical study of the AOS. The solver is based on the Landau–Lifshitz–Bloch equation that governs the dynamics of the magnetization coupled the microscopic three-temperature model, which describes the temporal evolution of the temperatures of the subsystems as caused by laser heating. The helicity-dependent magnetization switching is evaluated by a magnetooptical effective field caused by the inverse Faraday effect when a circularly polarized laser is applied to the sample. All the other usual terms of a full micromagnetic model are included (exchange, anisotropy, and Dzyaloshinskii–Moriya interaction). As a test, the model is used to describe the local magnetization switching of thin-film samples with high perpendicular anisotropy. The results are in a good agreement with available experimental observations. [ABSTRACT FROM AUTHOR]

Biomass is a spaceborn polarimetric P-band (435 MHz) synthetic aperture radar (SAR) in a dawn–dusk low Earth orbit. Its principal objective is to measure biomass content and change in all the Earth’s forests. The ionosphere introduces the Faraday rotation on every pulse emitted by low-frequency SAR and scintillations when the pulse traverses a region of plasma irregularities, consequently impacting the quality of the imaging. Some of these effects are due to total electron content (TEC) and its gradients along the propagation path. Therefore, an accurate assessment of the ionospheric morphology and dynamics is necessary to properly understand the impact on image quality, especially in the equatorial and tropical regions. To this scope, we have conducted an in-depth investigation of the significant noise budget introduced by the two crests of the equatorial ionospheric anomaly (EIA) over Brazil and Southeast Asia. This paper is characterized by a novel approach to conceive a SAR-oriented ionospheric assessment, aimed at detecting and identifying spatial and temporal TEC gradients, including scintillation effects and traveling ionospheric disturbances, by means of Global Navigation Satellite Systems ground-based monitoring stations. The novelty of this approach resides in the customization of the information about the impact of the ionosphere on SAR imaging as derived by local dense networks of ground instruments operating during the passes of Biomass spacecraft. The results identify the EIA crests as the regions hosting the bulk of irregularities potentially causing degradation on SAR imaging. Interesting insights about the local characteristics of low-latitudes ionosphere are also highlighted. [ABSTRACT FROM AUTHOR]

In the magneto-optical devices and sensors using the Faraday effect, maintaining the transmitted light intensity of a Faraday element is a key issue. A granular film with ferromagnetic fine metals dispersed in an insulator matrix has been expected to have both high transmittance and large Faraday effect. In this paper, we fabricated the Co–MgF2 granular film prepared by co-evaporation and investigated the effect of substrate heating temperature during co-evaporation and post-annealing on the transmittance and the Faraday rotation of the granular film. The Co–MgF2 granular film deposited at high substrate temperature was exhibited like a ferromagnetic behavior and high transmittance. Also, we found that the figure of merit [deg./dB], which was defined as a ratio of a Faraday rotation angle and decay of the transmitted light, was improved by post-annealing. [ABSTRACT FROM AUTHOR]

The Global Navigation Satellite System (GNSS) polarimetric effects on the propagation of radio occultations (ROs) are studied here. Polarimetric ROs have been suggested as a technique to detect heavy rain events using opportunity signals from GNSS satellites. The systematic effects that hinder the isolation of the precipitation information are described and their significance and separability are assessed. A method that relies on the received phase difference between polarizations is presented. A dual-frequency extension is capable to completely separate the hydrometeor information from the other effects, including the ionospheric influence. [ABSTRACT FROM AUTHOR]

The dependence of thermally induced depolarization on crystallographic axis orientation in crystal materials with negative optical anisotropy parameter in the presence of Faraday rotation has been analyzed. The orientation at which thermally induced depolarization is minimal has been found. The contributions to thermally induced depolarization of linear birefringence caused by photoelastic effect, of the temperature dependence of Verdet constant, and of the temperature dependence of optical anisotropy parameter are assessed. Three magneto-optical materials with negative optical anisotropy parameter have been compared with a currently widely used TGG crystal from the viewpoint of their prospective application in Faraday devices for powerful laser radiation. It has been demonstrated that these magneto-optical materials are undoubtedly superior to a TGG crystal. [ABSTRACT FROM AUTHOR]

Faraday rotation can be significant at L-band and needs to be considered in remote sensing from space using the spectrum window at 1.413 GHz protected for passive observations. This is especially so for a conical scanner such as SMAP because the variation of the rotation angle with position around the scan is of the same order of magnitude as the change with geographic position as the sensor travels in its orbit around the globe. Furthermore, the angle retrieved in situ by the radiometer is particularly noisy over land raising additional issues for remote sensing of soil moisture. Research is reported here assessing the magnitude of the problem and suggesting an approach for treating Faraday rotation in the context of remote sensing of soil moisture with a conical scanner like SMAP. [ABSTRACT FROM AUTHOR]

The ionospheric propagation path delay is a major error source in synthetic aperture radar (SAR) interferograms and, therefore, has to be estimated and corrected. Various methods can be used to extract different kinds of information about the ionosphere from SAR images, with different accuracies. This paper presents a general technique, based on a Bayesian inverse problem, that combines various information sources in order to increase the estimation accuracy, and thus the correction. A physically realistic fractal modeling of the ionosphere turbulence and a data-based estimation of the model parameters allow the avoidance of arbitrary filtering windows and coefficients. To test the technique, the differential ionospheric phase screen was estimated by combining the split-spectrum method with the azimuth mutual shifts between interferometric pair images. This combination is convenient since it can benefit from the strengths of both sources: range and azimuth variations from the split-spectrum method and small-scale azimuth variations from more sensitive azimuth shifts. Therefore, the two methods can recover the long and short wavelength components of the ionospheric phase screen, respectively. A theoretical comparison between the Faraday rotation method and the split-spectrum method is also reported. For the use in the combination, precedence was then given to the split-spectrum method because of the comparable precision level, lower susceptibility to biases, and wider applicability. Finally, Advanced Land Observing Satellite Phased Array type L-band SAR L-band images are used to show how the combined result is more accurate than that obtained with the simple split-spectrum method. [ABSTRACT FROM PUBLISHER]

This paper focuses on analytical methods of a finite-element method (FEM)-based edge heating system. The edge heating system plays a role in maintaining the temperature in the hot rolling process of carbon steel. Carbon steel moves along the production line and maintains the temperature by the edge heating system in the process. Power-of-the-edge heating system is transmitted to carbon steel during the process. Eddy currents are generated in carbon steel by Faraday’s law of electromagnetic induction, and eddy current loss serves as a heat source to increase the temperature. Thus, there is a need for accurate electromagnetic-field analysis and thermal analysis because the eddy current path generated in carbon steel greatly affects the heat distribution in carbon steel. This multiphysics analysis requires high reliability. Accordingly, this paper presents a coupling analysis method using an FEM-based coordinate mapping method as a more accurate analytical method. This paper also established an analytical approach to the edge heating system using the ductility analytical method of this coordinate mapping method. [ABSTRACT FROM AUTHOR]

We present a theoretical investigation of the polarization plane rotation at light transmission—Faraday effect, through 1-D multilayered magneto-photonic systems consisting of periodically distributed magnetic and dielectric layers. We calculate Faraday rotation (FR) spectra of photonic-magnonic crystals, where cell (or supercell) is composed of magnetic layer and dielectric layer (or section of dielectric photonic crystal). We found that the FR of p-polarized incident light is increasing in the transmission band with the number of magnetic supercells. The increase of FR is observed also in vicinity of the band-gap modes localized in magnetic layers but the maximal polarization plane rotation angles are reached at minimal transmittivity. We show that presence of linear magneto-electric interaction in the magnetic layers leads to significant increase of the FR angles of s-polarized incident light in the vicinity of the fine-structured modes inside the photonic-band-gap. [ABSTRACT FROM AUTHOR]

We introduce a nonreciprocal nongyrotropic magnetless metasurface. In contrast to previous nonreciprocal structures, this metasurface does not require a biasing magnet, and is therefore lightweight and amenable to integrated circuit fabrication. Moreover, it does not induce Faraday rotation, and hence does not alter the polarization of waves, which is a desirable feature in many nonreciprocal devices. The metasurface is designed according to a Surface-Circuit-Surface architecture and leverages the inherent unidirectionality of transistors for breaking time reversal symmetry. Interesting features include transmission gain as well as broad operating bandwidth and angular sector operation. It is finally shown that the metasurface is bianisotropic in nature, with nonreciprocity due to the electric-magnetic coupling parameters, and structurally equivalent to a moving uniaxial metasurface. [ABSTRACT FROM AUTHOR]

Polarimetric target decomposition is the most commonly used method of extracting information from polarimetric synthetic aperture radar (SAR) images. Coherent target decomposition methods are usually suitable for high-resolution images. Recently, Paladini reviewed coherent target decomposition methods and proposed a new approach, lossless and sufficient target decomposition (LSTD), using the special unitary matrix SU(4). However, this method suffers from parameter dependence and commutation problems that could introduce errors in parameter estimation such as an erroneous odd–even bounce ratio. In order to overcome these problems, a new model to decompose the circular polarization scattering vector is proposed. In this paper, the model applies a mapping from SU(4) to SU(6) to simplify the target representation while meaningful parameters, which are independent, can be extracted. Fully polarimetric L-band UAVSAR data are used to validate the proposed method. The most important odd–even bounce ratio parameter is used to compare the estimation accuracy between the proposed method and LSTD. Results show that the proposed method can extract parameters more accurately. [ABSTRACT FROM PUBLISHER]

Optical current transducers (OCTs) have clear advantages over conventional current transformers. To better understand the OCT performance, a basic OCT model is developed using finite-element analysis. To model an open-core OCT, the Faraday rotation and detection is implemented in the COMSOL Multiphysics. This paper introduces two experimental setups, which can be used for studying OCT performances under ac and dc excitations. The measured data agree with simulation results and validate the proposed model. The presented model can be developed to study different nonideal effects, in order to identify and mitigate noise sources in OCTs. [ABSTRACT FROM PUBLISHER]

Compact polarimetric (CP) synthetic aperture radar (SAR) systems are attracting increasing interest as they possess the ability to construct quad-polarimetric information with advantages of simpler system, lower data rate, and wider swath, compared to a fully polarimetric (FP) system. In order to get undistorted polarimetric information, calibration of CP measurements has to be performed. Freeman and Chen both proposed methods for CP SAR calibration using merely calibrators, which require at least three calibrators at a range line and would require many more calibrators when monitoring the change of the system across the swath is necessary. It has been proved that FP SAR calibration methods exploring scattering characteristics of natural distributed targets (DTs) can reduce the requirement of the number of deployed calibrators. However, it is much more complicated in the case of CP SAR calibration, as only two channels of CP measurements are available. This paper proposes a numerical CP calibration method using natural DTs and only one corner reflector (CR) for a reciprocal CP SAR system. The validity of the method for three typical CP modes is confirmed by simulations with Advanced Land Observing Satellite Phased Array L-band SAR data. Through sensitivity analysis, a dihedral at 0 ^\circ is selected as the best CR for the calibration algorithm. [ABSTRACT FROM PUBLISHER]

This paper analyzes a mechanism for the remote optical measurements of magnetic field variations above the surface of seawater. This magnetometry mechanism is based on the polarization rotation of reflected polarized laser light, in the presence of the earth’s magnetic field. Here the laser light is reflected off the surface of the water and off an underwater object. Two mechanisms responsible for the polarization rotation are the surface magneto-optical kerr effect (SMOKE) and the Faraday effect. In both the mechanisms, the degree of polarization rotation is proportional to the earth’s local magnetic field. Variations in the earth’s magnetic field due to an underwater object will result in variations in the polarization rotation of the laser light reflected off the water’s surface (SMOKE) and off the underwater object (Faraday effect). An analytical expression is obtained for the polarization-rotated field when the incident plane wave is at arbitrary angle and polarization with respect to the water’s surface. We find that the polarization rotated field due to SMOKE is small compared with that due to the Faraday effect. [ABSTRACT FROM AUTHOR]

On the example of yttrium–iron garnet films on a nonmagnetic substrate, the results of measurements of the magnetization relation to the crystal compression (stretching) stress due to the bending deformation of a substrate are presented. The measurements were performed by passing radiation in a waveguide structure formed by the magnetooptical crystal film on a gadolinium–gallium garnet substrate using the Faradey effect. Parallel magnetization sensitivity (1.5–1.7) \times \,\, 10^\mathrm -5 Am ^\mathrm -1 Pa ^\mathrm -1~ to stress is obtained, with stress at range ±6 MPa. Research was made at a bias magnetic field of 350 and 600 A/m. [ABSTRACT FROM AUTHOR]

Faraday rotation is an important issue for remote sensing of parameters such as soil moisture and ocean salinity, which are best done at low microwave frequency (e.g., L-band). Modern instruments such as the radiometer on the Soil Moisture and Ocean Salinity (SMOS) satellite and the Aquarius radiometers include polarimetric radiometer channels specifically to implement a correction for Faraday rotation. This works well over ocean, but it is known that over inhomogeneous scenes, such as a land/water mixture, significant errors can occur. This is a particularly important issue for the newest L-band sensor in space, the radiometer on the Soil Moisture Active Passive (SMAP) satellite, where the goal is remote sensing over land (soil moisture) and where the conical scan induces rapid variation in Faraday rotation. Analysis is presented here of the issues associated with retrieving Faraday rotation using the SMAP geometry and antenna pattern. It is shown that, in addition to scenes with a mixture of land and water, scenes with significant vegetation canopy are also associated with large errors in the retrieved Faraday rotation. Examples from the SMAP radiometer support the analysis. [ABSTRACT FROM PUBLISHER]

A correction methodology for distortions induced by ionospheric scintillation on fully polarimetric synthetic aperture radar (SAR) data is proposed. The correction is based on deriving the phase distortion induced by the ionosphere from Faraday rotation estimates. The estimated phase distortion is then used for correction. In order to compensate the phase and time–Doppler history distortions, the correction has to be performed at the slant range of the ionospheric layer, i.e., on partially focused single-look complex data. Accordingly, the performance of the proposed correction methodology depends, among other factors, on knowledge of the altitude of the effective ionospheric layer (assuming the thin ionospheric layer model). Its estimation from the SAR data itself is therefore also addressed. The methodology was applied and validated on simulated P-band data for various ionospheric conditions and on real L-band data acquired by the Advanced Land Observation Satellite Phased Array L-band SAR (PALSAR). [ABSTRACT FROM PUBLISHER]

In this paper, we study the nonreciprocal TE–TM mode conversion phenomenon by the simulation of magnetophotonic crystal fiber (MPCF). This MPCF consists of a periodic triangular lattice of air holes filled with magnetic fluid (Fe3O4) into a terbium gallium garnet (TGG) fiber. It is well known that, owing to its excellent transparency properties and its resistant character to laser damage, TGG is always selected as a Faraday rotator material. Also, TGG has a high Verdet constant related to the Faraday rotation (FR) effect. Here, with the consideration of the effect of gyrotropy, our simulations are associated with some calculations of the FR and modal birefringence. In this MPCF, the light is guided by internal total reflection, like classical fibers. However, it is shown that the designed MPCF could function as a mode converter with much stronger conversion efficiency than the conventional fibers. [ABSTRACT FROM AUTHOR]

In this paper, a high-dynamic and high-precise optical current measurement system based on the Faraday effect is presented. First, the sensor concept is presented and different sensor constructions are analyzed. Then, a measurement system based on a rare-earth iron garnet film is investigated. The measurement system uses multiple signal processing channels to increase the signal-to-noise ratio. Furthermore, the measurement range exceeds a rotation of 180° and therefore requires a counting mechanism to count the number of rotations. Finally, the precision of the presented system is analyzed. The precision is determined to be 4.9 ppm at a rotation range of 3300°. [ABSTRACT FROM PUBLISHER]

Magnetoactive materials are of considerable current interest, primarily for applications in nonreciprocal Faraday devices used for polarization control, optical isolation, optical switching, and modulation. The need for such devices is growing with laser power enhancement. They reduce risk of self-excitation of the amplifiers and optical elements damage and are a handy tool for organizing multipass schemes. However, at high average power of radiation these devices are subject to thermally induced effects that impair their operability and lead to increased losses and to the formation of phase distortions in the transmitted radiation. One of the methods to reduce thermally induced effects is to use in Faraday devices new magnetoactive materials with better thermo-optical properties. This paper is devoted to the study of thermo-optical and magneto-optical characteristics of a unique magnetoactive material—a terbium scandium aluminum garnet (TSAG) crystal. The TSAG has an extraordinary value of optical anisotropy parameter $\xi $ , a Verdet constant 25% higher than the traditionally used terbium gallium garnet crystal and the highest magneto-optical figure-of-merit known in magnetoactive materials at the moment. [ABSTRACT FROM AUTHOR]

In this paper, a numerical method optimizer based on covariance matching is proposed for synthetic aperture radar (SAR) polarimetric calibration. The method makes use of the information provided by a distributed target and a corner reflector in order to jointly estimate the system polarimetric distortion parameters and the Faraday rotation. A preliminary analysis is conducted to show the expected accuracy values and to identify the intrinsic ambiguities of the problem. Results from simulations are shown to assess the accuracy and convergence of the method. Finally, tests have been conducted on stack of repeated full polarimetric ALOS PALSAR images to check the stability of the retrieved distortion parameters in a realistic case. [ABSTRACT FROM PUBLISHER]

A method based on crossed polarizers to observe high-contrast coherent population trapping (CPT) resonance has been developed. Because crossed polarizers have a simple optical system, our method is suitable for chip-scale atomic clocks (CSACs). In CPT, the Faraday rotation in a linearly polarized light field (lin||lin) was calculated using two pairs of ?-system models; the spectrum of the Faraday rotation is also estimated. After measuring the contrast and linewidth with the crossed-polarizer method, a comparison of the theoretical model and experimental data showed they were in good agreement. Moreover, the experimental results showed that a high contrast (88.4%) and narrow linewidth (1.15 kHz) resonance could be observed using a Cs gas cell and D1-line verticalcavity surface-emitting laser (VCSEL). [ABSTRACT FROM AUTHOR]

We report about magneto-optical studies of magnetization reversal processes and magnetic domain structures in rare-earth Bi-substituted iron garnets in a wide temperature range. Measurements were done by a standard magneto-optical technique in Faraday geometry. Changes of both hysteresis loops shape and magnetic domain structures with temperatures indicate the presence of the branching domain structures above 130 K and the compensation temperature at 96 K. [ABSTRACT FROM AUTHOR]

In this paper, a novel fiber-based magnetooptic (MO) latching circuit using a bismuth-substituted yttrium iron garnet (Bi:YIG) is presented. Experimentation shows that nearly 90° of rotation of the state of polarization of incident light occurs between material latching states upon application of an external magnetic field greater than 500 G. This amount of rotation is enough to cause sufficient routing at the output of an optical interferometer of Sagnac configuration, which is presented in this paper. Due to the high coercivity of the Bi:YIG, the material remains in its magnetized state for very long periods of time and is thus latched. Reversing the applied magnetic field changes the state of the material, unlatching it. This capability has great importance for nonreciprocal all-optical devices requiring low power operation. In addition, having such control of the state of the nonreciprocal elements can allow for a wider diversification of small-scale and large-scale optical network design. A discussion of the experimental setup, the resulting measurement data, and its implication for future low power applications is presented. [ABSTRACT FROM AUTHOR]

A cryogenic Faraday isolator based on terbium-gallium garnet (TGG) ceramics has been designed and studied in experiments. Its performance capabilities at the laser radiation power of 435 W are demonstrated, and our models suggest that the isolator should perform up to 2 kW. Thermal effects-thermally induced depolarization and thermal lens in the TGG ceramics in the 89-293 K temperature range are investigated. It is shown that the TGG ceramics compares well to the TGG monocrystal as a medium for Faraday isolators, including cryogenic ones. At the same time, in contrast to the TGG monocrystal, ceramics allows creating large-aperture Faraday isolators for lasers with high-average and high-peak power. [ABSTRACT FROM AUTHOR]

Spaceborne linearly polarimetric synthetic aperture radar (SAR) provides information about surface properties and scatterer types by measuring the covariances between images formed using orthogonally polarized radio waves. However, ionospheric Faraday rotation (FR) and system calibration errors alter the balance in the polarimetric channels and distort the covariance matrix. Since FR angles are greater at lower radio frequencies, this paper focuses on the Biomass satellite, which is the European Space Agency's 7th Earth Explorer mission and will carry a P-band (435 MHz) polarimetric SAR. Its primary objective is to measure forest biomass density by combining estimates derived from the polarimetric covariance matrix with estimates based on measuring forest height with polarimetric interferometry and exploiting height-biomass allometric relations. The accuracy of four methods for estimating FR from polarimetric SAR is assessed using simulated images of forest with a range of biomass densities and system errors (H/V channel imbalances, antenna crosstalk, and noise) and over a large spread of FR angles. All methods have biases dependent on the FR, the relative phases of the crosstalk components, and the channel imbalance phase. The best performing method estimates FR to better than 5 ° under worst case system errors at all FR angles, so the accuracy of biomass density estimates should not be significantly affected. However, crosstalk phases are predicted to vary greatly across the Biomass antenna beam, and this could potentially cause the FR bias to vary by several degrees across the swath. These effects may occur even for the small values of FR met in L-band data. [ABSTRACT FROM PUBLISHER]

Detailed demagnetization process depending on various external field profiles has been investigated using a magneto-optical Kerr/Faraday microscopy for a Co/Pt multilayer film with a perpendicular magnetic anisotropy. By quantitatively analyzing local magnetic domain structures, we propose that it is possible to define a parameter $\eta$ , which represents how well the demagnetization has been carried out microscopically. The degree of demagnetization $\eta$ , defined by a ratio between the final demagnetized image intensity and saturated image intensity, has been experimentally found to significantly reflect the microscopic demagnetization behavior. Dependences of $\eta$ on the maximum amplitude, decreased step size, and effective sweeping rate of alternating demagnetizing field have been systematically investigated together with a direct microscopic observation of magnetic domain structures. [ABSTRACT FROM AUTHOR]

Faraday isolators for high average power lasers operating at room temperature are surveyed. Three devices on [001] oriented TGG crystals with the most known optical schemes are considered: traditional scheme, and schemes with compensation of thermally induced depolarization inside magnetic field and outside magnetic field. We report a unique 30-mm-aperture Faraday isolator with thermally induced depolarization compensation inside magnetic field. It provides 33.5-dB isolation ratio at 1.5-kW average laser power. [ABSTRACT FROM AUTHOR]

The validity of the flux rule to determine the electromotive force in a cycle, \cal E=-d\Phi/dt, has been the subject of a large amount of controversy since the beginning of electrical technology. Although most authors reach correct conclusions for a class of problems called Faraday paradoxes, the arguments that are used vary and often rely on ad-hoc physical reasoning. A didactic and insightful treatment should be based solely on Maxwell's equations, the constitutive laws, and a detailed study of the mathematics involved. [ABSTRACT FROM AUTHOR]

A brief historical review is made of the 180-year-old debate on Faraday’s unipolar inductor. By introducing two convenient modifications of Faraday’s original experiment of 1832, pertinent answers are experimentally found to the most debated problems: 1) Can Faraday’s law be used? Yes; 2) Do the magnetic field lines rotate when the magnet rotates? No. 3) Can the seat of induction be unambiguously determined? Yes. 4) Is there a fundamental difference between rotational and translational motional induction? Yes: the “edge effect”, whereby a negative v\timesB field appears whenever a magnetic edge moves perpendicularly to itself. An additional experiment is presented to verify the theory. Finally, 5) Can Relativity Theory be applied? The Special Theory, no; the General one, yes. [ABSTRACT FROM PUBLISHER]

A rapid magneto-optical (MO) spectrometer is introduced. In conventional MO measurements, a monochromator produces quasimonochromatic incident light. The MO spectrum is then found by measuring the hysteresis loop at each wavelength in small steps, which is time consuming. In contrast, the new system uses 1) incident white light, 2) polarization rotation by a Faraday cell and spectroscopic detection using an area sensor, and 3) subtraction of spectra for small changes of polarization. By this method, an MO spectrum can be measured in only a few minutes with a single sweep of the magnetic field, enabling rapid exploration of the magnetic properties of a wide variety of materials. [ABSTRACT FROM AUTHOR]

The present study was designed to explore a novel method of electromagnetic control of cellular activity of aquatic organisms by utilizing a strong magnetic field and weak current stimulation. Three kinds of aquatic organisms, Chlamydomonas pumilio, Daphnia pulex, and Hydra, were exposed to 10 T magnetic fields, and the effects of applying weak electric currents at several milli-amperes on the transmission of polarized light on aquatic organisms at 550 nm was measured. Under ambient fields, the transmission of polarized light was not changed by the electric currents. However, in the presence of a 10 T magnetic field, a strong change in the transmission was observed during and after the electrical stimulation. It was speculated that the cellular components, having both mechanical flexibility and a higher charge density, were affected by the Lorentz force that was generated by the weak electric current and the strong magnetic field. The results indicated that the combination of a 10 T magnetic field and weak stimulation at a mA current level was effective for the measurement and control of the viability of aquatic organisms. [ABSTRACT FROM AUTHOR]