六角光晶格中稳定的高电荷离散涡旋

Discrete vortex solitons and PT symmetry

We study the effect of lifting the degeneracy of vortex modes with a PT symmetric defect, using discrete vortices in a circular array of nonlinear waveguides as an example. When the defect is introduced, the degenerate linear vortex modes spontaneously break PT symmetry and acquire complex eigenvalues, but nonlinear propagating modes with real propagation constants can still exist. The stability of nonlinear modes depends on both the magnitude and the sign of the vortex charge, thus PT symmetric systems offer new mechanisms to control discrete vortices.

Simultaneous creation of multiple vortex-antivortex pairs in momentum space in photonic lattices

Engineering of the orbital angular momentum (OAM) of light due to interaction with photonic lattices reveals rich physics and motivates potential applications. We report the experimental creation of regularly-distributed quantized vortex arrays in momentum space by probing the honeycomb and hexagonal photonic lattices with a single focused Gaussian beam. For the honeycomb lattice, the vortices are associated with Dirac points and mimic the Berry curvature sources. However, we show that the resulting spatial patterns of vortices are strongly defined by the symmetry of the wave packet evolving i…

离散与半离散多维孤子和涡旋：已有成果与新发现

Discrete and semi-discrete multidimensional solitons and vortices: Established results and novel findings

本文综述了基于离散非线性薛定谔方程及其推广的离散与半离散非线性模型，以及这些模型产生的各类二维、三维多维离散孤子与涡旋模式的理论和实验研究成果。

Solitons and Vortices in Two-dimensional Discrete Nonlinear Schrodinger Systems with Spatially Modulated Nonlinearity

We consider a two-dimensional (2D) generalization of a recently proposed model [Phys. Rev. E 88, 032905 (2013)], which gives rise to bright discrete solitons supported by the defocusing nonlinearity whose local strength grows from the center to the periphery. We explore the 2D model starting from the anti-continuum (AC) limit of vanishing coupling. In this limit, we can construct a wide variety of solutions including not only single-site excitations, but also dipole and quadrupole ones. Additionally, two separate families of solutions are explored: the usual "extended" unstaggered bright solit…

Geometric frustration in polygons of polariton condensates creating vortices of varying topological charge

Vorticity is a key ingredient to a broad variety of fluid phenomena, and its quantised version is considered to be the hallmark of superfluidity. Circulating flows that correspond to vortices of a large topological charge, termed giant vortices, are notoriously difficult to realise and even when externally imprinted, they are unstable, breaking into many vortices of a single charge. In spite of many theoretical proposals on the formation and stabilisation of giant vortices in ultra-cold atomic Bose-Einstein condensates and other superfluid systems, their experimental realisation remains elusiv…

Composite vortices in nonlinear circular waveguide arrays

It is known that, in continuous media, composite solitons with hidden vorticity, which are built of two mutually symmetric vortical components whose total angular momentum is zero, may be stable while their counterparts with explicit vorticity and nonzero total angular momentum are unstable. In this work, we demonstrate that the opposite occurs in discrete media: hidden vortex states in relatively small ring chains become unstable with the increase of the total power, while explicit vortices are stable, provided that the corresponding scalar vortex state is also stable. There are also stable m…

Off-Axis Spiral Phase Mirrors for Generating High Intensity Optical Vortices

In this work, we present a novel and practical method for generating optical vortices in high-power laser systems. Off-axis spiral phase mirrors are used at oblique angles of incidence in the beam path after amplification and compression allowing for the generation of high-power optical vortices in almost any laser system. An off-axis configuration is possible via modification of the azimuthal gradient of the spiral phase helix and is demonstrated with a simple model using a discrete spiral staircase. This work presents the design, fabrication, and implementation of off-axis spiral phase mirro…

光致光子晶格中离散涡旋孤子的观测

Observation of discrete vortex solitons in optically-induced photonic lattices

首次在二维光致光子晶格中观测到了离散涡旋孤子。我们证明了在自聚焦非线性介质中晶格对光学涡旋的强稳定性，并研究了一类广义奇异光束产生离散涡旋的过程。

Antiferromagnetic phase transition in the temperature-dependent NIR-VUV dielectric function of hexagonal YMnO$_3$

Hexagonal YMnO$_3$ is well known for the co-occurrence of ferroelectricity and antiferromagnetism at low temperatures. Using temperature-dependent spectroscopic ellipsometry at an $a$-plane oriented single crystal, we show how the dielectric function is affected by the magnetic order transition at the Néel temperature. We focus especially on the pronounced charge transfer transitions around (1.6-1.7)eV which are strongly connected to Mn 3$d$ electrons. If described with a Bose-Einstein model, the temperature dependency of their energy and broadening is characterized by effective phonon energie…