Nonuniform Polarization Research Articles

φ0 -Josephson junction in twisted bilayer graphene induced by a valley-polarized state

Recently, gate-defined Josephson junctions in magic angle twisted bilayer graphene (MATBG) were studied experimentally and highly unconventional Fraunhofer patterns were observed. In this work, we show that an interaction-driven valley-polarized state connecting two superconducting regions of MATBG would give rise to a long-sought-after purely electric controlled $\varphi_0$-junction in which the two superconductors acquire a finite phase difference $\varphi_0$ in the ground state. We point out that the emergence of the $\varphi_0$-junction stems from the valley-polarized state which breaks time-reversal symmetry and trigonal warping effects which break the intravalley inversion symmetry. Importantly, a spatially non-uniform valley polarization order parameter at the junction can explain the highly unconventional Fraunhofer patterns observed in the experiment. Our work explores the novel transport properties of the valley-polarized state and suggests that gate-defined MATBG Josephson junctions could realize the first purely electric controlled $\varphi_0$-junctions with applications in superconducting devices.

Longitudinal evolution from scalar to vector beams assembled from all-dielectric metasurfaces.

Vector vortex beams (VVBs) with non-uniform polarization states have a wide range of applications, from particle capture to quantum information. Here, we theoretically demonstrate a generic design for all-dielectric metasurfaces operating in the terahertz (THz) band, characterized as a longitudinal evolution from scalar vortices carrying homogeneous polarization states to inhomogeneous vector vortices with polarization singularities. The order of the converted VVBs can be arbitrarily tailored by manipulating the topological charge embedded in two orthogonal circular polarization channels. The introduction of the extended focal length and the initial phase difference effectively guarantees the smoothness of the longitudinal switchable behavior. A generic design approach based on vector-generated metasurfaces can assist in the exploration of new singular properties of THz optical fields.

Quantitative detection of high-order Poincaré sphere beams and their polarization evolution.

The high-order Poincaré sphere (PS) introduces a mapping whereby any vector beams with spatially homogeneous ellipticity are represented by a specific point on the surface of the sphere. We propose the quantitative detection of high-order PS beams by introducing three sets of nonuniform polarization bases in the high-order Stokes parameters. Overall polarization detection is realized by directly separating and measuring the respective intensity of different nonuniform polarization bases based on S-plate. The polarization evolution of the PS beams on the high-order PS and between the conventional and the high-order PS are achieved by S-plate. The results provide new insights for the generation, evolution and detection of arbitrary beams on the high-order PS.

Propagation properties of partially coherent array beams with a non-uniform polarization

We study a new class of partially coherent array beams with a non-uniform polarization, named radially polarized Gaussian Schell-model array (RPGSMA) beams and analyze the reliability conditions for the array beams based on the unified theory of coherence and polarization, Moreover, the statistical properties of such beam propagating in free space are investigated in detail. It is found that, the propagation properties of the RPGSMA beams are closely related to initial beam parameters. With an appropriate choice of the beam parameters, the average intensity will evolve into optical lattice patterns, and the degree of coherence (DOC) from the lattice distribution on the original plane evolves into a Gaussian profile in the far field, and the degree of polarization (DOP) appears a periodical grid-like distribution on propagation. These results may be beneficial to particle trapping and free-space optical communications.

Active non-uniform illumination-based underwater polarization imaging method for objects with complex polarization properties.

Active polarization imaging is one of the most effective underwater optical imaging methods that can eliminate the degradation of image contrast and clarity caused by macro-molecule scattering. However, the non-uniformity of active illumination and the diversity of object polarization properties may decrease the quality of underwater imaging. This paper proposes a non-uniform illumination-based active polarization imaging method for underwater objects with complex optical properties. Firstly, illumination homogenization in the frequency domain is proposed to extract and homogenize the natural incident light from the total receiving light. Then, the weight values of the polarized and non-polarized images are computed according to each pixel's degree of linear polarization (DoLP) in the original underwater image. By this means, the two images can be fused to overcome the problem of reflected light loss generated by the complex polarization properties of underwater objects. Finally, the fusion image is normalized as the final result of the proposed underwater polarization imaging method. Both qualitative and quantitative experimental results show that the presented method can effectively eliminate the uneven brightness of the whole image and obtain the underwater fusion image with significantly improved contrast and clarity. In addition, the ablation experiment of different operation combinations shows that each component of the proposed method has noticeable enhancement effects on underwater polarization imaging. Our codes are available in Code 1.

Specific resonance mode enhancement and suppression using non-uniform polarization of piezoelectric wafers: Theory and experiments

We present experimental demonstration of specific resonance mode enhancement and suppression in circular and rectangular piezoelectric wafers with engineered non-uniform polarization profiles. The polarization profiles are designed based on the electromechanical impedance response of non-uniformly polarized wafers as obtained from the theory. The circular wafers are fabricated with non-uniform polarization profiles that involve a central polarized region surrounded by an unpolarized region. The radius of the polarization zone is designed based on the condition for specific mode enhancement obtained from the electromechanical impedance response of non-uniformly polarized wafers. We actually show how the condition can not only be used to enhance but also to suppress electromechanical resonances. Two kinds of wafers are designed and fabricated to specifically suppress second and third radial modes respectively. Similarly, rectangular wafers are designed with two different kinds of non-uniform polarization profiles — the first of which enhances the second in-plane extensional mode in the impedance spectrum and the second polarization profile suppresses all the electromechanical resonances pertaining to the in-plane extensional modes and selectively excites only the in-plane bending modes. The proposed approach of using non-uniformly polarized wafers finds application in designing multi-frequency sensors/transducers, frequency-tuned receivers, acoustic beamforming, and other non-traditional applications such as information storage.

Estimation and removal of backscattered light with nonuniform polarization information in underwater environments.

The nonuniform of polarization information of backscattered light has always been a neglected characteristic in polarization underwater imaging, but its accurate estimation plays an important role in the quality of imaging results. Traditional polarization imaging methods assume that the degree of polarization and angle of polarization of backscattered light are constant. In fact, the polarization information of backscattering light is gradual, this assumption makes traditional methods work only in a small area of the camera's field of view, in which the change of the polarization information of backscattered light can be ignored. In this paper, by analyzing the distribution of backscattered light, it is concluded that its polarization information has the characteristics of low-rank. Then, the degree of polarization and angle of polarization of backscattered light were estimated by low-rank and sparse matrix decomposition, and the clear scene was reconstructed. Experimental results show that the proposed method breaks through the limitation of the assumption of backscattered light in traditional polarization imaging method, and expands the detection field under the same conditions, which makes it possible to develop polarization underwater imaging method to the direction of large field of view detection.

Critical Importance of Nonuniform Polarization and Fringe Field Effects for Scaled Ferroelectric FinFET Memory

The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) and high coercive field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> leads to a large MW is not always valid. For a large <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields.

Rancang Bangun Antena Mikrostrip MIMO 4 Elemen Untuk Komunikasi 5G Pada Frekuensi Band N40

This study discusses the design of the MIMO microstrip antenna which is implemented in a 5G communication system that works on the N40 frequency band (2.3-2.4 GHz) with the center frequency of 2.35 GHz. The parameters that are unique of this antenna is focusing on the mutual coupling and correlation of MIMO antennas. The MIMO configuration was chosen because it can meet the high data transmission needs of 5G communication systems. The antenna is composed of a square patch with a microstrip insert feed-line technique. Then, the substrate uses FR-4 material, with a dielectric constant value of 4.3. After the design of a single element antenna that works according to the criteria is obtained, then the antenna is arranged into a configuration of 4 parallel elements, a 2×2 MIMO configuration with uniform polarization, and a 2×2 MIMO configuration with non-uniform polarization. After the design process, the antenna design is fabricated and then measured using a Vector Network Analyzer (VNA). The analysed antenna parameters are return loss, mutual coupling, Voltage Standing Wave Ratio (VSWR), bandwidth, and radiation pattern. From the element measurement results, it is found that the return loss is -11.24 dB and the bandwidth is 70 MHz at the center frequency of 2.35 GHz. As for the analysis of mutual coupling between elements, the best results were obtained from the MIMO configuration of 2×2 non-uniform polarization with values -20 dB for all elements. The antenna measurement results obtained indicate a similarity with the simulation results. This result is suitable for MIMO applications that require very low mutual coupling and correlation between elements.

Asymmetrical spiral spectra and orbital angular momentum density of non-uniformly polarized vortex beams in uniaxial crystals

To explore the effect of non-uniform polarization on orbital angular momentum (OAM) in anisotropic medium, in this work investigated are the evolution of the spiral spectra and OAM densities of non-uniformly polarized vortex (NUPV) beams in uniaxial crystals propagating orthogonal to the optical axis, and also the case of uniformly polarized vortex (UPV) beams with left-handed elliptical polarization. In the input plane, the NUPV beams present their spiral spectra of m-mode concentrated at m = l ± 1 modes rather than m = l mode, and reveal the relation among topological charge l, mode of spiral spectra m and the power weight value Rm expressed by . The relation is still satisfied for UPV beams in uniaxially anisotropic crystals, whereas for NUPV beams their relations are no longer valid owing to non-uniform polarization. Furthermore, the analysis indicates that the asymmetrical distribution of power weight of spiral spectra and the non-zero value in the sum of longitudinal OAM densities originate from the initial non-uniform polarization and anisotropy in uniaxial crystals rather than topological charges. In addition, the relation between spiral spectrum and longitudinal OAM density is numerically discussed. This work may provide an avenue for OAM-based communications, optical metrology, and imaging by varying the initial non-uniform polarization.

Color image encryption using vectorial light field through a compact optical set-up

Vector light fields have spatially non-uniform polarization across the transverse plane. In this study, a color image encryption scheme has been proposed in which the data is encoded into the spatially varying polarization states of light to achieve higher degrees of freedom. This scheme provides a strong security and a straightforward way for optical implementation. Simulation and experimental results have been presented to verify the feasibility of the proposed scheme.

Transversely oriented cylindrically polarized optical fields.

Cylindrical vector (CV) beams have nonuniform polarization vector distribution with a singularity line directed along the optical axis. In this paper, we propose a method to synthesize transversely oriented cylindrically polarized optical fields in the focal region with a singularity line perpendicular to the optical axis. The scheme is based on the time-reversal method, the vectorial diffraction theory, and the 4Pi optical configuration. Both transversely oriented radially polarized and azimuthally polarized optical fields are demonstrated. The superposition of transverse cylindrically polarized optical fields leads to a peculiar distribution carrying controllable transverse spin angular momentum (SAM) and transverse orbital angular momentum (OAM) that may find applications in optical tweezing, light-matter interaction, and unidirectional beam propagation excitation.

Analysis and experimental demonstration of propagation features of radially polarized specific non-uniformly correlated beams.

With the development of the unified theory of coherence and polarization, the novel physical properties generated by different correlation structures of vector partially coherent beams (PCBs) have attracted much attention. Recently, a new class of structured beams have been proposed [Opt. Lett.45, 3824 (2020)10.1364/OL.397316], called vector specific non-uniformly correlated beams. These beams combine non-uniform polarization and non-uniform correlation, and they exhibit propagation features not seen in conventional vector PCBs. In this Letter, we continue the analysis of the previous work, taking radially polarized Hermite non-uniformly correlated (RPHNUC) beams as an example, and focus on the physical interpretation of the peculiar propagation features of such beams. We verify the predicted behavior of RPHNUC beams through experiment.

Tuning the Relative Strengths of Electromechanical Resonances Using Non-Uniform Polarization of Piezoelectric Wafers

Tuning the Relative Strengths of Electromechanical Resonances Using Non-Uniform Polarization of Piezoelectric Wafers

Modeling fluid polarization during flow in a non-uniform polarization field

A sample will undergo T1 relaxation at continuously changing applied magnetic field strengths when flowing from the Earth magnetic field outside an NMR instrument to the much stronger applied magnetic field inside an NMR instrument. The interaction between fluid flow, T1 relaxation and magnetic field distributions in the case of negligible T1 dispersion can be described by considering two length scales involved: the characteristic polarization length vT1, and the effective polarization magnet length Lm⁎. By comparing water flow experiments on a 0.9 m long Halbach magnet array with simulations using the Bloch-Torrey equation, we determined that Lm⁎ is given by the integral along flow direction x of the normalized axial polarization field distribution, p(x) = B0(x)/B0(xROI), in which xROI is the center of the polarization magnet. The fluid magnetization level Mz in a region-of-interest located at xROI is a function of the ratio s = vT1/Lm⁎ and can be generally expressed as Mz,ROI = M0⁎(s)[1–exp(-1/2 s)]. The effective equilibrium magnetization function M0⁎(s) was found to have both a sample independent contribution from the axial polarization field p(x) and a sample dependent contribution from the flow velocity profile at a given flow rate. In our experiments, the axial Halbach field was found to contribute with a weight of approximately 1/3 to M0⁎(s) and the remaining 2/3 wt is contributed by the flow velocity distribution. Based on this analysis, a set of general principles for magnetization build up modeling and online NMR instrument design has been derived.

Polarization-based intensity correlation of a depolarized speckle pattern

A different kind of intensity correlation, denoted as polarization-based intensity correlation (PBIC), is proposed and demonstrated to investigate the correlation between different polarizations of a depolarized speckle pattern (DSP), which has non-uniform spatial polarization distribution. It is shown both theoretically and experimentally that the range of the PBIC for any polarization of the DSP depends on the spatial average intensity of the speckles corresponding to that particular polarization. The experimentally determined nature of the change of the range of the PBIC for different polarization components, due to the variation in the average intensity, is found to be matching well with the theoretical prediction. The existence of non-zero correlation between two orthogonally polarized speckle patterns, filtered from a partially DSP, is also observed. This study may be useful in exploiting the PBIC for different applications such as speckle cryptography.

Polarization states and Stokes vortices of dual Butterfly-Gauss vortex beams with uniform polarization in uniaxial crystals

We propose dual Butterfly-Gauss vortex beams with uniform polarization, which are composed of two finite-energy Butterfly-Gauss beams with vortex cores. Based on the paraxial vector theory, the analytical propagation expressions of the proposed beams in uniaxial crystals orthogonal to the optical axis are derived and used to investigate the evolutions of autofocusing behavior, polarization states and Stokes vortices. The results show that the autofocusing behavior and its autofocusing length can be affected by topological charge, and the input uniform polarization is disordered into non-uniform polarization owing to anisotropic diffraction. The symmetry and rotation of polarization states are also found for the case of vortex. The Stokes parameters on the Poincaré sphere can be manipulated by adjusting the refractive index ratio, azimuthal angle and phase retardation angle. Their Stokes vortices, e.g. S12 vortices, present the behavior of merging, separation and reversal. The presented work may be useful for manipulating polarization dynamics of catastrophe optical field in uniaxial crystal and has potential values in polarization-sensitive detection.

Enhancement of second harmonic microscopy images in collagen-based thick samples using radially polarized laser beams

The visualization of collagen-based tissues imaged with second harmonic generation (SHG) microscopy strongly depends on the polarization state of the scanning laser beam. This has been often explored using spatially homogeneous states (mainly linear or circular). However, vector beams (i.e. laser beams with spatially non-uniform polarization states) have become a powerful tool in different research field and technological applications. In particular, radially polarized vector beams are known to provide a tight focal spot and lateral resolution enhancement. Here we propose the use of radially polarized beams to improve the quality of SHG microscopy images. The performance of this particular type of vector beam is compared to that obtained with a circularly polarized light beam for different non-stained specimens and depth locations. Results show that independently of the sample’s thickness, the efficiency of SHG processes is increased when using the radially polarized beam, also leading to a higher image quality. Our results open the route for using vector beams to get a better visualization of biological details within the imaged areas, especially at deeper locations.

Compound Vector Light Generator Based on a Metasurface

In view of wide applications of vector light with a non-uniform polarization state, a compound vector light generator is proposed to generate compound vector light. One compound vector light contains two or more non-uniform polarization modes and several annular intensities, which can carry more polarization information and possess higher dimensional singularity. The proposed compound vector light generator consists of cross nanoholes with high polarization conversion efficiency; it works under linear polarized light, and the mode of the generated compound vector light can be adjusted through rotating cross nanoholes. The structure parameters of the compound vector light generator are optimized with the aid of numerical simulation, and the simulation results for the generated light fields verify the performance of the proposed device. The advancement of the compound vector light and metasurface design of the compound vector light generator can assist in the exploration of novel singular properties of light fields and the broadening of applications of vector light fields.

Coupling Analysis of Flexoelectric Effect on Functionally Graded Piezoelectric Cantilever Nanobeams.

The flexoelectric effect has a significant influence on the electro-mechanical coupling of micro-nano devices. This paper studies the mechanical and electrical properties of functionally graded flexo-piezoelectric beams under different electrical boundary conditions. The generalized variational principle and Euler–Bernoulli beam theory are employed to deduce the governing equations and corresponding electro-mechanical boundary conditions of the beam model. The deflection and induced electric potential are given as analytical expressions for the functionally graded cantilever beam. The numerical results show that the flexoelectric effect, piezoelectric effect, and gradient distribution have considerable influences on the electro-mechanical performance of the functionally graded beams. Moreover, the nonuniform piezoelectricity and polarization direction will play a leading role in the induced electric potential at a large scale. The flexoelectric effect will dominate the induced electric potential as the beam thickness decreases. This work provides helpful guidance to resolve the application of flexoelectric and piezoelectric effects in functionally graded materials, especially on micro-nano devices.