arXiv subjects

Hexiang He

Publications and source records attributed to Hexiang He.

8 recordsLinked to original sources

arXiv2025

Chiral solitons in quadratic quasi-phase-matched photonic crystals

We introduce a quasi-phase-matched technique in quadratic nonlinear crystals, constructing an artificial gauge field by changing the inclination angle of stripes, which is realized by the positive and negative polarization directions of nonlinear susceptibility along the crystal. Unlike the artificial gauge field constructed through linear coupling in other settings, the gauge field in this system is realized by nonlinear coupling. We demonstrate that this gauge field can generate stable chiral solitons with chiral energy flow rotating around the solitons. In contrast to conventional chiral currents generated with the same specie or frequency, the chiral currents in the present system are formed by mutual coupling between fundamental frequency and second harmonic components. We derive the semi-analytical solution for the chiral energy flow in this system. It is found that there exists an optimal inclination angle that can maximize the chiral energy flow under different parameters, and this optimal inclination shows a positive correlation with the power and detuning. The mobility and collisions of the chiral solitons are also discussed. The results show that chiral solitons move in response to kicking and undergo fully elastic collisions with each other. In addition, the possibility of experimentally generating chiral solitons and chiral currents is outlined.

physics.optics↗

arXiv2025

Vortex solitons in quasi-phase-matched photonic crystals with the third harmonic generation

We report stable composite vortex solitons in the model of a three-dimensional photonic crystal with the third-harmonic (TH) generation provided by the quasi-phase-matched quadratic nonlinearity. The photonic crystal is designed with a checkerboard structure in the $\left( x\text{,}% y\right) $ plane, while the second-order nonlinear susceptibility, $d(z)$, is modulated along the propagation direction as a chains of rectangles with two different periods. This structure can be fabricated by means of available technologies. The composite vortex solitons are built of fundamental-frequency (FF), second-harmonic (SH), and TH components, exhibiting spatial patterns which correspond to vortex with topological charges $s=1$, a quadrupole with $s=2$, and an anti-vortex structure with $s = -1$, respectively. The soliton profiles feature rhombic or square patterns, corresponding to phase-matching conditions $\varphi =0$ or $\pi $, respectively, the rhombic solitons possessing a broader stability region. From the perspective of the experimental feasibility, we show that both the rhombic and square-shaped composite vortex solitons may readily propagate in the photonic crystals over distances up to $\sim 1$ m. The TH component of the soliton with $s=\mp 1$ is produced by the cascaded nonlinear interactions, starting from the FF vortex component with $s=\pm 1$ and proceeding through the quadrupole SH one with $s=2$. These findings offer a novel approach for the creation and control of stable vortex solitons in nonlinear optics.

physics.optics↗

arXiv2022

Vortex solitons in quasi-phase-matched photonic crystals

We report solutions for stable compound solitons in a three-dimensional quasi-phase-matched photonic crystal with the quadratic ($\chi ^{(2)}$) nonlinearity. The photonic crystal is introduced with a checkerboard structure, which can be realized by means of the available technology. The solitons are built as four-peak vortex modes of two types, rhombuses and squares (intersite- and onsite-centered self-trapped states, respectively). Their stability areas are identified in the system's parametric space (rhombuses occupy an essentially broader stability domain), while all bright vortex solitons are subject to strong azimuthal instability in uniform $\chi^{(2)}$ media. Possibilities for experimental realization of the solitons are outlined.

physics.optics↗

arXiv2021

Geometric phase with full-wedge and half-wedge rotation in nonlinear frequency conversion

When the quasi-phase matching (QPM) parameters of the $χ^{(2)}$ nonlinear crystal rotate along a closed path, geometric phase will be generated in the signal and idler waves that participate in the nonlinear frequency conversion. In this paper, we study two rotation schemes, full-wedge rotation, and half-wedge rotation, of the QPM parameters in the process of fully nonlinear three-wave mixing. These two schemes can effectively suppress the uncertainty in creating the geometric phase in the nonlinear frequency conversion process when the intensity of the pump is depleted. The finding of this paper provides an avenue toward constant control of the geometric phase in nonlinear optics applications and quantum information processing.

physics.optics↗

arXiv2018

Excited states of two-dimensional solitons supported by the spin-orbit coupling and field-induced dipole-dipole repulsion

It was recently found that excited states of semi-vortex and mixed-mode solitons are unstable in spin-orbit-coupled Bose-Einstein condensates (BECs) with contact interactions. We demonstrate a possibility to stabilize such excited states in a setting based on repulsive dipole-dipole interactions induced by a polarizing field, oriented perpendicular to the plane in which the dipolar BEC is trapped. The strength of the field is assumed to grow in the radial direction $\sim $ $r^{4}$. Excited states of semi-vortex solitons have vorticities $S$ and $S+1$ in their two components, each being an eigenstate of the angular momentum. They are fully stable up to $S=5$. Excited state of mixed-mode solitons feature interweaving necklace structures with opposite fractional values of the angular momentum in the two components. They are stable if they are built of dominant angular harmonics $\pm S$, with $S\leq 4$. Characteristics and stability of these two types of previously unknown higher-order solitons are systematically analyzed. Their characteristic size is $\sim 10$ $\mathrm{μ}$m, with the number of atoms $\lesssim 10^{5}$

cond-mat.quant-gas↗

arXiv2017

3D Object Imaging through Scattering Media

Human ability to visualize an image is usually hindered by optical scattering. Recent extensive studies have promoted imaging technique through turbid materials to a reality where color image can be restored behind scattering media in real time. The big challenge now is to recover a 3D object in a large field of view with depth resolving ability. Here, we reveal a new physical relationship between speckles generated from objects at different planes. With a single given point spread function, 3D imaging through scattering media is achieved even beyond the depth of field (DOF). Experimental testing of standard scattering media shows that the original DOF can be extended up to 5 times and the physical mechanism is depicted. This extended 3D imaging is expected to have important applications in science, technology, bio-medical, security and defense.

physics.optics↗

arXiv2017

Imaging objects through scattering layers and around corners by retrieval of the scattered point spread function

We demonstrate a high-speed method to image objects through a thin scattering medium and around a corner. The method employs a reference object of known shape to retrieve the speckle-like point spread function of the scatterer. We extract the point spread function of the scatterer from a dynamic scene that includes a static reference object, and use this to image the dynamic objects. Sharp images are reconstructed from the transmission through a diffuser and from reflection off a rough surface. The sharp and clean reconstructed images from single shot data exemplify the robustness of the method.

physics.optics↗

arXiv2017

Cross-symmetry breaking of two-component discrete dipolar matter-wave solitons

We study the spontaneous symmetry breaking of dipolar Bose--Einstein condensates trapped in stacks of two-well systems, which may be effectively built as one-dimensional trapping lattices sliced by a repelling laser sheet. If the potential wells are sufficiently deep, the system is modeled by coupled discrete Gross--Pitaevskii equations with nonlocal self- and cross-interaction terms representing dipole--dipole interactions. When the dipoles are not polarized perpendicular or parallel to the lattice, the cross-interaction is asymmetric, replacing the familiar symmetric two-component solitons with a new species of cross-symmetric or -asymmetric ones. The orientation of the dipole moments and the interwell hopping rate strongly affect the shapes of the discrete two-component solitons as well as the characteristics of the cross-symmetry breaking and the associated phase transition. The sub- and super-critical types of cross-symmetry breaking can be controlled by either the hopping rate between the components or the total norm of the solitons. The effect of the interplay between the contact nonlinearity and the dipole angle on the cross-symmetry breaking is also discussed.

nlin.PS↗