Cross-polarized Phase Research Articles

Dynamic bifunctional THz metasurface via dual-mode decoupling

Metasurfaces have powerful light field manipulation capabilities and have been researched and developed extensively in various fields. With an increasing demand for diverse functionalities, terahertz (THz) metasurfaces are also expanding their domain. In particular, integrating different functionalities into a single device is a compelling domain in metasurfaces. In this work, we demonstrate a functionally decoupled THz metasurface that can incorporate any two functions into one metasurface and switch dynamically through external excitation. This proposed metasurface is formed by the combination of split-ring resonators and phase change material vanadium dioxide ( VO 2 ). It operates in the single-ring resonant mode and double-ring resonant mode with varying VO 2 in insulating and metallic states, respectively. More importantly, the phase modulation is independent in two operating modes, and both cover a 360° cross-polarized phase with efficient polarization conversion. This characteristic makes it obtain arbitrary independent phase information on the metasurface with different modes to switch dual functions dynamically. Here, we experimentally demonstrate the functions of a tunable focal length and large-angle focus deflection of a THz off-axis parabolic mirror to verify the dual-function switching characteristics of the functionally decoupled metasurface. The functionally decoupled metasurface developed in this work broadens the way for the research and application of multifunctional modulation devices in the THz band.

Broadband transmissive amplitude-and-phase metasurface for vortex beam generation and hologram

Transmissive electromagnetic metasurfaces that allow for the independent and simultaneous control of the cross-polarized phase and amplitude responses are presented. On varying the square split ring opening and orientation angles, the cross-polarized transmission response allows for full phase and amplitude coverage and exhibits broadband characteristics. Because of the designed amplitude-and-phase units, the metasurfaces allow for complex field manipulations over a wide frequency band. Representative applications of the proposed metasurfaces include (1) the generation of a high-purity vortex beam (with Chebyshev amplitude distribution) and (2) the realization of metasurface holography with two imaging planes over a wide frequency band. The measurement results agreed well with those of full-wave simulations, thus confirming the feasibility and effectiveness of the proposed approach, which is suitable for designing advanced, broadband field-manipulation systems.

Model-Based Decomposition of Dual-Pol SAR Data: Application to Sentinel-1

In this study, we advance a new family of model-based decompositions adapted for dual-pol synthetic aperture radar data. These are formulated using the Stokes vector formalism, coupled to mappings from full quad-pol decomposition theory. A generalized model-based decomposition is developed, which allows separation of an arbitrary Stokes vector into partially polarized and polarized wave components. We employ the widely used random dipole cloud as a volume model but, in general, nondipole options can be used. The cross-polarized phase <inline-formula> <tex-math notation="LaTeX">$\delta $ </tex-math></inline-formula>, and the <inline-formula> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> angle, which is a function of the ratio between wave components, measure the transformation of polarization state on reflection. We apply the decomposition to dual-pol data provided by Sentinel-1 (S1) covering different scenarios, such as agricultural, forest, urban, and glacial land-ice. We show that the polarized term of received polarization state is not usually the same as the transmitted one, and can therefore be used for key applications, e.g., classification and geo-physical parameter estimation. We show that, for vegetated terrain, depolarization is not the only influencing factor to S1 backscattered intensities and, in the case of vertical crops (e.g., rice), this allows the crop orientation effects to be decoupled from volume scattering in the canopy. We demonstrate that coherent dual-pol systems show strong phase signatures over glaciers, where the polarized contribution significantly affects the backscattered state, resulting in elliptical polarization on receive. This is a key result for S1, for which dual-pol phase analysis coupled to dense time series offer great opportunities for land-ice monitoring.

Recent progresses of circular polarization multiplexing engineered multi-functional metasurfaces

In this paper, the recent progresses of circular polarization (CP) multiplexing engineered multi-functional metasurfaces is reviewed. Firstly, in order to break through the physical limitation introduced by the conjugate symmetric geometric phases responses under orthogonal CP incidences, the equivalent Jones matrix of metasurface model is derived and the independent manipulation method of two cross-polarized phase responses is proposed. Furthermore, the three-channel wave-front integration method based on metasurface is proposed based on amplitude and phase relationship between co- and cross-polarized output components, which achieves the full manipulation of transmitted CP electromagnetic energy. On these basis, the concept of chirality-assisted phase and the wave-front manipulation method for all full CP channels is proposed, which enhances the utilization efficiency of CP electromagnetic energy. The results proposed in this paper can pave the solid theoretical foundation for increasing the capability of information channels and transmission rate.

Spurious Signal in SMAP Fourth Stokes Parameter

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.

Broadband polarization-dependent coding metasurface for reflection manipulation

In this paper, a method for broadband polarization-dependent coding metasurface design is proposed. Single-polarized unit cells are employed due to their single-polarized phase manipulation with little effect on cross-polarized phase in broadband. The equivalent circuit of these unit cells is developed to analyze the mechanism. Because of single-polarized phase manipulation, coding metasurfaces for different polarizations can be designed separately. The polarization-dependent coding metasurface can be obtained by simply combining them into a sharing aperture. Simulated and measured results prove that our method offers a simple and effective strategy for broadband polarization-dependent metasurface design.

Vector dark solitons in a single mode fibre laser

We report on the first experimental observation of vector dark solitons in an erbium-doped single mode fiber ring laser. We show experimentally that two orthogonal linearly polarized dark solitons could couple together incoherently through the cross polarization phase modulation and form a bound state of dark solitons. In particular, the formed vector dark solitons are stable even under existence of high frequency periodic background intensity modulation. Numerical simulations have well confirmed the existence of vector dark solitons in single mode fiber lasers and their stability under periodic background intensity modulation.©2018 Optical Society of America OCIS codes: (190.4370) nonlinear optics, fibers; (190.5530) pulse propagation and temporal solitons.

Observation of vector solitons supported by third-order dispersion

We report on the experimental observation of dark-bright and antidark-bright vector solitons supported by third-order dispersion in a weakly birefringent cavity fiber laser. Using a cavity dispersion and birefringence management technique we constructed a weakly birefringent cavity fiber laser with near-zero net cavity dispersion. Operating the fiber laser in either the net normal or net anomalous dispersion regime, we found that both dark-bright and antidark-bright vector solitons could be simultaneously formed as a result of incoherent cross-polarization phase modulation. Our experimental results confirm the existence of antidark-bright vector solitons and the coexistence of dark-bright and antidark-bright vector solitons in a real physical system.

Ultra-thin and -broadband microwave magnetic absorber enhanced by phase gradient metasurface incorporation

Based on the effect of anomalous reflection and refraction caused by the circularly cross-polarized phase gradient metasurface (PGM), an ultra-thin and -broadband composite absorber composed of metasurface and conventional magnetic absorbing film is proposed and demonstrated in this paper. In the case of keeping nearly the same thickness of absorbing layer, the equivalent thickness of magnetic absorbing film is enlarged by the effect of anomalous reflection and refraction, resulting in the expansion and improvement of the absorbing bandwidth and efficiency in low microwave frequency. A biarc metallic sub-cell for circularly crossed polarization is adopted to form a broadband phase gradient, by the means of rotating the Pancharatnam–Berry phases. As indicated in the experimental results, the fabricated 3.6 mm-thick absorber can averagely absorb microwave energy with the specular reflection below −10 dB in the frequency interval of 2–12 GHz, which shows a good match with simulated results. Due to ultra-thin thickness and ultra-wide operating bandwidth, the proposed application of PGM in absorbing can provide an alternative way to enhance the absorbing property of current absorbing materials.

Complementary bilayer metasurfaces for enhanced terahertz wave amplitude and phase manipulation

Manipulation of terahertz wave by metasurfaces has shown tremendous potential in developing compact and functional terahertz optical devices. Here, we propose complementary bilayer metasurfaces for enhanced te-rahertz wave amplitude and phase manipulation. The metasurfaces are composed of one layer of metal cut-wire arrays and one layer of their complementary aperture arrays separated by a dielectric spacer. Through the near-field coupling between transverse magnetic resonances in the metal apertures and electric resonances in the metal cut-wires, the structures can manipulate the cross polarization conversion and phase dispersion of terahertz wave. Particularly, the designed metasurfaces demonstrate a phase delay of 180° between two orthogonal axes with the same transmission amplitude between 0.70 and 1.0 THz, enabling a 45° broadband polarization conversion. When the metal cut-wires are rotated with respect to the apertures or the thickness of the dielectric spacer is changed, the amplitude and phase dispersion of the transmitted terahertz wave can be tuned. Such complementary coupled bilayer metasurfaces offer a new method to control the amplitude and phase dispersion of terahertz wave and promise great potential for applications in terahertz meta-devices.

Statistical Distributions of the Copolarized and Cross-Polarized Phase Differences of Stratified Media

We determine the statistical distributions of the copolarized and cross-polarized phase differences of fields scattered from a stack of two 2-D rough interfaces in any observation plane. This communication is carried within the framework of the first-order small perturbation method. The probability laws are established for Gaussian distributions of heights and for infinite extension interfaces. We show that, outside the incidence plane, the cross-polarized phase difference is not uniformly distributed and contains information about the stratified medium.

A wideband deflected reflection based on multiple resonances

We propose to realize wideband deflected reflection in microwave regime through multiple resonances. A wideband deflected reflection of a phase gradient metasurface is designed using a double-head arrow structure, which has demonstrated an ultra-wideband cross-polarized reflection caused by multiple electric and magnetic resonances. The wideband effect benefits from the wideband cross-polarized reflection and flexible phase modulation of the double-head arrow structure. Simulated and experimental results agree well with theoretical predictions. Furthermore, relative bandwidths of deflected reflection reach to 71 % for both x- and y-polarized waves under normal incidence. Our method of expansion bandwidth may pave the way in many practical applications, such as RCS reduction, stealth surfaces.

Relating statistical characteristics of cross-polarized phase difference to speckle noise

A qualitative relationship between the statistical behavior of cross-polarized phase difference ϕ hvvh and dominant noise type is examined based on the polarimetric noise model proposed. The noise model focusing on the covariance matrix is able to separate the multiplicative noise which only affects the amplitude from the additive noise that alters both the amplitude and phase. In the case of low noise, the phase is not affected by the noise and ϕ hvvh distribution is predicted to be centered at 0 deg in terms of reciprocity theorem. The case of strong noise is much more complicated as the dominant noise type plays an important role in the statistics of ϕ hvvh . The phase over the area where multiplicative noise dominates is not altered, thus the ϕ hvvh distribution is expected to have similar behaviors to the case of low noise. However, the dominant additive noise would significantly affect the phase so that an obvious deviation from 0 deg for ϕ hvvh distribution is expected. Experiments with Radarsat-2 full polarimetric imageries further validate this qualitative relationship.

Antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer (I): Derivation of the antenna temperature equation

Spaceborne polarimetric microwave correlation radiometer is a new type of instrument for the passive microwave remote sensing from space, which can provide an important way for remote sensing of sea surface wind vector and other ocean atmosphere environmental parameters. Antenna cross-polarization correction is an important part of the data pre-processing algorithm. In this paper, for the demand of antenna cross-polarization correction in spaceborne polarimetric microwave correlation radiometer, we have independently derived the full polarization antenna temperature equation based on the polarization coherent detection theory and the definition of Stokes parameters. The equation for the four parameters of Stokes antenna temperature introduced the cross polarization amplitude and phase between the Stokes parameters. Besides, the influence of the polarization rotation angle on the antenna pattern computation was considered. Finally, we established a geometric correspondence between the antenna scanning beam and the earth scene. The principle for determining the parameters of the antenna temperature equation was also discussed. Stokes antenna temperature equation laid the foundation for antenna cross-polarization correction for spaceborne polarimetric microwave correlation radiometer in the future.

Solid-state magnetic resonance studies of polyaniline as a radical scavenger

The first detailed study of polyaniline (PANI) and reduced PANI (R-PANI) before and after reaction with the stable organic free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) by using solidstate13C CP MAS (cross-polarization magic-angle spinning), NQS (nonquaternary suppressed) and CPPI (cross-polarization phase inversion) nuclear magnetic resonance techniques is reported. These techniques reveal relatively subtle structural changes that occur upon reaction with DPPH free radicals and confirm the radical scavenging ability of PANI. The integrated intensity of the PANI CP MAS spectrum after reaction with DPPH is about 8% larger than that of PANI and this cannot be explained by an oxidation process alone. The increase is attributed to a decrease in the polaron concentration in the polymer, which is consistent with electron paramagnetic resonance (EPR) data that show a decrease of the EPR signal intensity after reaction of chemically synthesized PANI with DPPH.

Observation of stimulated orientational scattering and cross-polarized self-starting phase conjugation in a nematic liquid-crystal film

We have observed stimulated extraordinary-ordinary wave scattering and cross-polarized self-starting optical phase conjugation effects in a nematic liquid-crystal film. The basic mechanism involved is the nonresonant laser-induced nematic crystal axis reorientation. These processes require low optical power and are characterized by millisecond response speed.

Novelty Filtering Using Phase Conjugate Wave in Organic Dye-Doped Polymer Films

A real-time detection of a moving object was demonstrated by taking the subtraction between cross-polarized phase conjugate waves with fast and slow response times with two kinds of dye-doped phase conjugators. One consists of superposed films of an erythrosin-B-doped film and a methyl-orange-doped film, and the other is a film dispersed with both dyes. The relative phase between cross-polarized phase conjugate waves by the both dye-dispersed films was stable.

Fluctuations of Differential Phase and Radar Measurements of Precipitation

Abstract The specific differential polarization phase shift KDP has been suggested as a possible estimator of rainfall as well as a rain-hail discriminator in several recent studies. Here, the complex multivariate Gaussian model, used widely in communication theory and statistics optics, is applied for modeling KDP caused by precipitation. Specifically, the width of the marginal phase probability density function is used to estimate ϕDP (cumulative differential phase) fluctuations. This results in suboptimal but simple expressions, which highlight the dependence of ϕDP fluctuations on the magnitude of the HV (horizontal–vertical) cross-correlation coefficient |ρHV|. Statistical arguments are separated from the effects of radar wavelength and Doppler spread. Implications of ϕDP fluctuations on accuracy of rainfall and snow/hail radar measurements are also discussed and the author comments on the feasibility of using cross-polarized differential phase measurements.

A theoretical formula for the prediction of cross-polarized signal phase

An approximate theoretical formula for the prediction of cross-polarized signal phase relative to co-polar signal is presented. In the formula, the phase of cross-polarized signal induced by rain is related to rainfall rate or rain-induced attenuation. The relation is derived by calculating the forward scattering amplitudes of the Pruppacher-Pitter type raindrops at 33 frequencies ranging from 3 to 40 GHz. The dependence of the relation on raindrop-size distribution is also discussed.

Aperture efficiency for paraboloidal reflectors

The definition and formulas for cross polarization, phase error, and illumination efficiency given by Ludwig and Thomas are shown to not always account for the correct cross polarization and phase error loss. New definitions and formulas are proposed that give a better separation of the losses associated with cross-polarized radiation, phase errors, and nonuniform aperture illumination.