3D Polarization Research Articles

A welding seam positioning method based on polarization 3D reconstruction and linear structured light imaging

Aiming at the current welding seam tracking problems such as susceptibility to arc light interference, low work efficiency, and poor real-time performance, a single-frame large-field welding seam positioning method combining polarization three-dimensional (3D) reconstruction and linear structured light imaging is proposed. Calculate the surface polarization state of the welding area through the polarization intensity images in four directions, use the degree of polarization and polarization angle to calculate the surface normal vector and integrate to obtain the relative depth value. Design a centerline extraction method based on skeleton extraction and Random Sample Consensus (RANSAC) to obtain the three-dimensional coordinates of the laser stripe. The three-dimensional coordinates of the laser fringe and the relative depth value of the polarization three-dimensional reconstruction are combined to calculate the real three-dimensional point cloud of the weld and the welded part. With this method, only a single frame of image data is acquired prior to welding and the coordinates of the 3D scene within the large field of view of the polarisation camera can be calculated, so there is no interference from arc light. For the weld within 100 mm, the 3D positioning accuracy is 0.2502 mm, which meets the requirements of weld positioning.

Phase field model for cell spreading dynamics.

We suggest a 3D phase field model to describe 3D cell spreading on a flat substrate. The model is a simplified version of a minimal model that was developed in Winkler (Commun Phys 2:82, 2019). Our model couples the order parameter u with 3D polarization (orientation) vector field [Formula: see text] of the actin network. We derive a closed integro-differential equation governing the 3D cell spreading dynamics on a flat substrate, which includes the normal velocity of the membrane, curvature, volume relaxation rate, a function determined by the molecular effects of the subcell level, and the adhesion effect. This equation is easily solved numerically. The results are in agreement with the early fast phase observed experimentally in Dobereiner (Phys Rev Lett 93:108105, 2004). Also we find agreement with the universal power law (Cuvelier in Curr Biol 17:694-699, 2007) which suggest that cell adhesion or contact area versus time behave as [Formula: see text] in the early stage of cell spreading dynamics, and slow down at the next stages.

Computational polarization 3D: New solution for monocular shape recovery in natural conditions

Analyzing the polarimetric properties of the reflected light is a simple, fast, and low-cost approach to recover shape information, but no reported method can accurately recover surface shape from non-Lambertian object in natural conditions with a single view. Another major issue is the lack of effective methods to address azimuth ambiguity during the surface reconstruction. To address these two major obstacles, we propose a monocular 3D polarization imaging approach for non-Lambertian surfaces by investigating the subtle difference in specular and diffuse reflection and then separating them using independent component analysis (ICA). Separated pure diffuse reflection enables accurate polarization extraction, based on which a gradient field is derived to determine surface normals. The ambiguity is removed by solving an optimization problem with a reference gradient field. We experimentally demonstrate the performance of the proposed method with man-made objects under controlled illumination and human face under natural illumination.

Purity of 3D polarization.

Measures of purity for 3D partially polarized fields, and in particular, the separation into circularly and linearly polarized contributions, are reexamined, and a new degree of total linear polarization introduced. Explicit expressions for the characteristic decomposition in terms of coherency matrix elements are presented, including the special case of an intrinsic coherency matrix. Parameterization of the coherency matrix in terms of ellipticity, and the directions of the ellipse normal and major axis are investigated. Phase consistency is discussed. A comprehensive collection of results regarding intrinsic polarization properties is presented.

KCs2[Pb2Br5(HCOO)2]: A Polar 3D Lead‐Bromide Framework Exhibiting Strong Second‐Harmonic Generation Response

The discovery of new nonlinear optical (NLO) crystals with excellent properties is in urgently demand because of their ability to generate coherent light. Herein, we report an unique NLO lead bromide formate, KCs2 [Pb2 Br5 (HCOO)2 ], which has been synthesized by a mix-solvothermal method. KCs2 [Pb2 Br5 (HCOO)2 ] exhibits strong phase-matching second-harmonic generation (SHG) response (6.5×KDP), large birefringence (0.16@ 1064 nm), and a wide transparent window in most visible light and mid-IR region. Interestingly, KCs2 [Pb2 Br5 (HCOO)2 ] features a polar 3D lead-bromide framework in which adjacent Pb-Br layers containing coplanar Pb6 Br6 rings are not only parallel to each other, but also orient in the same direction. These oriented arrangements are responsible for the strong SHG response and large birefringence that are elucidated by both local dipole moment and theoretical calculations. This research provides a new strategy to explore subsequent NLO crystals.

Effect of polarimetric nonregularity on the spin of three-dimensional polarization states

While the spin of two-dimensional polarization states admits a simple representation, its physical interpretation for three-dimensional (3D) mixed polarization states requires a more involved analysis. In this work, we address the spin structure of the electric field of a general 3D polarization state by taking advantage of the characteristic decomposition and the recently introduced notion of nonregularity associated with 3D states. We show that a nonregular polarization state necessarily has an additional spin component due to the state’s genuinely 3D nature, and both the orientation and magnitude of the spin are regulated by the degree of nonregularity. The results provide new physical insight into partially polarized evanescent and tightly focused light fields in which strong nonregular character has recently been demonstrated.

Near-infrared monocular 3D computational polarization imaging of surfaces exhibiting nonuniform reflectance.

This paper presents a near-infrared (NIR) monocular 3D computational polarization imaging method to directly reconstruct the shape of surfaces exhibiting nonuniform reflectance. A reference gradient field is introduced to the weight constraints for globally correcting the ambiguity of the surface normal for a target with nonuniform reflectance. We experimentally demonstrated that our method can reconstruct the shape of surfaces exhibiting nonuniform reflectance in not only the near field but also the far field. Moreover, with the proposed method, the axial resolution can be kept constant even under different object distances as long as the ratio of the focal length to the object distance is fixed. The simplicity and robustness of the proposed method make it an attractive tool for the fast modeling of 3D scenes.

Fully-structured counter-propagating optical trap sculpted by spherical aberration

Aberrations of light are commonly known as undesired effects in different applications, including optical trapping. However, here we demonstrate how to take advantage of controlled spherical aberration in order to shape extended optical trapping landscapes, fully-structured in three-dimensional (3D) space and embedding transverse as well as longitudinal electric field contributions. We numerically analyze the light field customization by the simple means of including glass plates in a counter-propagating trapping configuration, presenting sculpted intensity as well as 3D polarization ellipse structures. Experimentally, we prove the realized counter-propagating optical structure by particle velocimetry as well as the analysis of scattered light of optically guided micro-particles. Finally, we demonstrate the potential of our approach by creating extended 3D particle assemblies.

Optical needles with arbitrary three-dimensional spin angular momentum.

Based on our previous research on optical needles with arbitrary three-dimensional (3D) polarization, we investigate the relationship between the electric field and spin angular momentum (SAM). We have realized optical needles with arbitrary 3D spin-orientation and SAM per photon. To our best knowledge, it is the first time to obtain optical needles whose SAM can be customized on both direction and size. The relative error between the obtained spin and customized spin is always less than 5% even if SAM per photon is very small.

Quasi-coherent noise-like pulses in a mode-locked fiber laser with a 3D rotatable polarization beam splitter.

For the first time, to the best of our knowledge, we experimentally observed a novel quasi-coherent noise-like pulse (NLP) in a simplified nonlinear polarization evolution mode-locking fiber laser when appropriate polarization was maintained for the lasing light through a three-dimensional rotatable polarization beam splitter inside the cavity. The degree of first-order coherence was evaluated after an interferogram measurement. The evolution of the measured shot-to-shot spectrum revealed that the NLPs possess quasi-coherence. Self-starting ultrafast soliton pulses switching to quasi-coherent NLPs at higher pump power levels were due to the preservation of the soliton features, mainly the Kelly sidebands in the spectrum. Quasi-coherent NLPs with average power of 56.58 mW and 10.4% slope efficiency were achieved with single pulse energy of 3.22 nJ.

Determinant parameters of surface morphology to corrosion behaviour of cold-rolled auto sheet steel

To elucidate the effect of surface morphology on corrosion behaviour of cold-rolled steel, three-dimensional (3D) surface profiles, average corrosion rate and potential differences (PD) for local areas of cold-rolled steel were investigated using a 3D white-light interference surface profilometer, polarization curves and atomic force microscope. Results showed that the linear relationship between surface roughness Sa and corrosion rate, achieved based on polished steels, was not valid for the as-received interstitial-free steels. An innovative surface parameter, the proportion of active area (Pa), was proposed and verified to have a distinct positive correlation with the corrosion rate of as-received cold-rolled steels. Moreover, it was found that the specimen with different surface textures were involved in diverse corrosion stages, and thus, the corrosion rate was determined by different surface parameters. As a result, a three-stage corrosion evolution, including initial dissolution (stage I), peak levelling (stage II) and general thinning (stage III), was deduced, in which Pa and local PD played predominant roles to stage I and stage II, respectively.

Growth of NiAl-Layered Double Hydroxide on Graphene toward Excellent Anticorrosive Microwave Absorption Application.

High‐performance microwave absorbers with special features are desired to meet the requirements of more complex modern service environments, especially corrosive environments. Therefore, high‐efficiency microwave absorbers with corrosion resistance should be developed urgently. Herein, a 3D NiAl‐layered double hydroxide/graphene (NiAl‐LDH/G) composite synthesized by atomic‐layer‐deposition‐assisted in situ growth is presented as an anticorrosive microwave absorber. The content of NiAl‐LDH in the composite is optimized to achieve impedance matching. Furthermore, under the cooperative effects of the interface polarization loss, conduction loss, and 3D porous sandwich‐like structure, the optimal NiAl‐LDH/G shows excellent microwave absorption performance with a minimum reflection loss of −41.5 dB and a maximum effective absorption bandwidth of 4.4 GHz at a loading of only 7 wt% in epoxy. Remarkably, the encapsulation effect of NiAl‐LDH can restrain the galvanic corrosion owing to graphene. The epoxy coating with the NiAl‐LDH/G microwave absorber on carbon steel exhibits long‐term corrosion resistance, owing to the synergetic effect of the superior impermeability of graphene and the chloridion‐capture capacity of the NiAl‐LDH. The NiAl‐LDH/G composite is a promising anticorrosive microwave absorber, and the findings of this study may motivate the development of functional microwave absorbers that meet the demands of anticorrosive performance of coatings.

Joint Dense 3D Reconstruction Method for Endoscopic Images of Weak Texture Scenes

Endoscopic inspection is an important non-destructive testing method. Traditional 3D endoscopic reconstruction methods, such as polarization reconstruction and shading reconstruction, have the drawbacks of not determining the object’s actual size and positional information. The stereo vision method is limited by its operating principles and has the issue of sparse reconstructed point clouds. These drawbacks greatly restrict the applications of the endoscope. Therefore, this work proposes a joint dense 3D reconstruction method for endoscopic images of weak texture scenes. This method uses the shading reconstruction normal to correct the polarization reconstruction normal, then uses coordinate conversion and point cloud fusion to convert the polarization and shading 3D reconstruction results from the pixel coordinate system to the world coordinate system. Finally combines the reconstruction results from the world coordinate system’s polarization, shading, and stereo vision. The fusion coefficients are obtained by solving the minimum error model, and then a complete and detailed 3D reconstruction surface was obtained in the world coordinate system. This method could avoid the difficulty of obtaining real coordinates for the 3D reconstruction of polarization and shading and prevent the issue of the sparse point cloud afforded by stereo vision reconstruction for weak texture scenes. The combined dense 3D reconstruction method had an average error of < 1% for length measurement of a 3D curve, which is highly significance for industrial endoscopic inspection.

Three-dimensional nonlinear photonic crystal in naturally grown potassium\u2013tantalate\u2013niobate perovskite ferroelectrics

Since quasi-phase-matching of nonlinear optics was proposed in 1962, nonlinear photonic crystals were rapidly developed by ferroelectric domain inversion induced by electric or light poling. The three-dimensional (3D) periodical rotation of ferroelectric domains may add feasible modulation to the nonlinear coefficients and break the rigid requirements for the incident light and polarization direction in traditional quasi-phase-matching media. However, 3D rotating ferroelectric domains are difficult to fabricate by the direct external poling technique. Here, we show a natural potassium–tantalate–niobate (KTN) perovskite nonlinear photonic crystal with spontaneous Rubik’s cube-like domain structures near the Curie temperature of 40 °C. The KTN crystal contains 3D ferroelectric polarization distributions corresponding to the reconfigured second-order susceptibilities, which can provide rich reciprocal vectors to compensate for the phase mismatch along an arbitrary direction and polarization of incident light. Bragg diffraction and broadband second-harmonic generation are also presented. This natural nonlinear photonic crystal directly meets the 3D quasi-phase-matching condition without external poling and establishes a promising platform for all-optical nonlinear beam shaping and enables new optoelectronic applications for perovskite ferroelectrics.

Polarization characteristic analysis of orthogonal reflectors with a side-scanning galvanometer in a laser communication terminal system.

An alignment tolerance allocation and alignment method of orthogonal reflectors with high polarization-maintaining characteristics is presented. A geometric optics vector model of orthogonal reflectors is established to derive the propagation vector of the output beam, including pitch angle error of the first mirror, the side-scanning angle of the galvanometer, and rotation angle error of the secondary mirror. The polarization transmission matrix of the orthogonal reflectors is derived based on the 3D polarization ray-tracing algorithm to present the relationship between assembly errors and diattenuation or retardance of the orthogonal reflectors. A calculation example of certain polarization ellipticity error is given to quantitatively distribute the orthogonal mirror assembly error. The optimal side-sway angle selection method of the galvanometer side-sway angle in a laser communication system is presented; further, effective measures to minimize the polarization ellipticity error is put forward.

Constraint-free wavelength conversion supported by giant optical refraction in a 3D perovskite supercrystal

Nonlinear response in a material increases with its index of refraction as n4. Commonly, n ~ 1 so that diffraction, dispersion, and chromatic walk-off limit nonlinear scattering. Ferroelectric crystals with a periodic 3D polarization structure overcome some of these constraints through versatile Cherenkov and quasi-phase-matching mechanisms. Three-dimensional self-structuring can also lead to a giant optical refraction. Here, we perform second-harmonic-generation experiments in KTN:Li in conditions of giant broadband refraction. Enhanced response causes wavelength conversion to occur in the form of bulk Cherenkov radiation without diffraction and chromatic walk-off, even in the presence of strong wave-vector mismatch and highly focused beams. The process occurs with a wide spectral acceptance of more than 100 nm in the near infrared spectrum, an ultra-wide angular acceptance of up to ±40∘, with no polarization selectivity, and can be tuned to allow bulk supercontinuum generation. Results pave the way to highly efficient and adaptable nonlinear optical devices with the promise of single-photon-to-single-photon nonlinear optics.

Anatomy of nerve fiber bundles at micrometer-resolution in the vervet monkey visual system.

Although the primate visual system has been extensively studied, detailed spatial organization of white matter fiber tracts carrying visual information between areas has not been fully established. This is mainly due to the large gap between tracer studies and diffusion-weighted MRI studies, which focus on specific axonal connections and macroscale organization of fiber tracts, respectively. Here we used 3D polarization light imaging (3D-PLI), which enables direct visualization of fiber tracts at micrometer resolution, to identify and visualize fiber tracts of the visual system, such as stratum sagittale, inferior longitudinal fascicle, vertical occipital fascicle, tapetum and dorsal occipital bundle in vervet monkey brains. Moreover, 3D-PLI data provide detailed information on cortical projections of these tracts, distinction between neighboring tracts, and novel short-range pathways. This work provides essential information for interpretation of functional and diffusion-weighted MRI data, as well as revision of wiring diagrams based upon observations in the vervet visual system.

Detection of DG-islanding employing decision boundary of polarization ellipse parameters

This article presents a mathematical equations-based approach for islanding detection of distributed generations (DGs). To develop the proposed method, first, a set of mathematical expressions, characterizing the dynamics of electrical quantities during islanding situations, are selected; the quantities are: deviation of rotor angle, frequency and rate-of-change-of-frequency (RoCoF). Second, these electrical quantities are transformed into three-dimensional (3D) Polarization Ellipse (PE) domain, which yields five parameters, namely, azimuth, elevation, tilt angles, semi-minor and semi-major axes. Finally, an equation of decision boundary (DB) is developed to classify between the islanding events and non-islanding incidents. An extensive assessment of the proposed method is carried out considering the critical test cases which include surplus or shortage of real/reactive power mismatch situations that may exist during islanding. The presence of different load-types, with various quality factors, is also accounted for the test. A large number of islanding events and non-islanding disturbances, such as, capacitor switching, load switching, temporary faults, etc., are simulated in real-time using the model of a practical distribution network developed in Opal-RT digital platform. The proposed approach is critically assessed using F-measure technique and the assessment emphasize the selection of the method as a potential tool for detection of DG-islanding.

Polarimetric dimension and nonregularity of tightly focused light beams

Polarimetric dimension and nonregularity are newly introduced concepts that characterize three-dimensional (3D) polarization states of light. We analyze the spectral polarimetric dimension and the degree of nonregularity associated with two kinds of tightly focused beams: a radially fully polarized Gaussian Schell-model (GSM) beam and a partially polarized beam composed of an incoherent superposition of two orthogonally polarized (coherent) plane-wave modes. We show that for both beams the focal field can exhibit genuine 3D and nonregular character, with even perfect nonregularity encountered for the tightly focused two-mode beam. These features originate from the partial spatial coherence and partial polarization of the incident beams, and in the limit of full coherence and polarization the three-dimensionality and nonregularity of the focal field vanish. We also find that the GSM beam can generate a nanoscale region around the focus where the field is essentially 3D unpolarized. The results demonstrate the rich polarimetric structure of focal fields and may find uses in optical particle manipulation and sensing.

Optical needles with arbitrary homogeneous three-dimensional polarization.

We propose a new method to generate optical needles by focusing vector beams comprised of radially polarized component and azimuthally polarized vortex components. The radial part can generate longitudinal polarization, while the azimuthal parts can generate left- and right-handed polarization. Hence, an arbitrary 3D polarization can be obtained. To our knowledge, it may be the first time that arbitrarily polarized optical needles whose transverse sizes are under 0.5λ have been achieved. The polarized homogeneity of the needles is beyond 0.97.